Tipitaka are not conflict, but the inexpert readers often make them conflict.

1. I can completely say mostly "imaginable conflict" is not an actual conflict. I uncountable questions on the internet through more than 10 years and I discover the fact it's reader's error.
2. The case, sutta, is just used in a case, not wrong in the right case, but it is going to be wrong in the different case. Four Nikaya means there are more than ten thousand cases. In my experience, almost conflicts come from the readers' error, not from Tipitaka or Atthakatha.
3. The case's environment has various properties which can be noticed by just the proficient.
4. It is very hard to be a real Theravada professor. In VN Atthakatha has written it requires 20 years experience, the memory of whole 5 canons of Vijaya, and the whole 4 Nikaya. After that one has memorized that all, he are going to have the understanding like KN, Abhidhamma, and Atthakatha. By this way, most of "imaginable conflicts" are becoming no conflict.
5. All of the western style professors have no above qualifications, so they can't understand Abhidhamma, Atthakatha, and some sutta, then they again them all. It means they against the Tipitaka origin because actually, the MahaAtthakatha teachers are the first council members.

Lord Yama's identity

I've been reading up on cosmology and am curious if Lord Suyama of Yama heaven and Lord Yama as judge of the recently deceased are the same figure. The latter is often said to reside in either the hell or preta realms, but since he is also a vaimanikapreta, I can't help but wonder if his time in the higher planes equates to this third level of heaven. Or are the same names simply coincidence?
Any thoughts/sources are much appreciated.

It is in the dependent origination.
SuyamaDeva born by KusalaVipakaCitta, wholesome resultant, only. That citta is the resultant consciousness, viññāṇa, of the wholesome frabrication, sańkhaāra.
YamaVemanikaPeta born by AkusalaVipakaCitta, unwholesome resultant, only. That citta is the resultant consciousness of wholesome frabrication.
They are completely different.
Only one karma creates all life-basis-resultants (patisandhi, bhavanga, cuti, karmaja-matter) per each rebirth of one whole life however there are many karma cause the resultant citta at the other six senses of life, except those patisandhi, bhavanga, cuti, which created by only one same karma.

Why Buddha lined up four brahmavihara in the chronological order 'metta, karuna, mudita and upeksha'

The practitioner wishes to let the being took the benefit&happiness, lovingkindness, so the practitioner wishes to help that being when that being is suffering, wishes to congratulate with that being when he is happy, and is equanimity when whatever happen.

Upekka, equanimity, is not easier than the other three. The practitioner is ignoring, doing not care, when he practices Upekkha without practicing the other three before, i.e. the healthy practitioner is not equanimity but he is ignoring when he doesn't care the standing old woman on the bus while he is sitting.

See the path of purification brahmavihāraniddesa:

1. Ñ(IX,109): One who wants to develop these four should practice them towards beings first as the promotion of the aspect of benefit—and lovingkindness has the promotion of the aspect of benefit as its characteristic;
2. Ñ: and next, on seeing or hearing or judging that beings whose benefit has been thus wished for are at the mercy of suffering, they should be practiced as the promotion of the aspect of the removal of suffering—and compassion has the promotion of the aspect of the removal of suffering as its characteristic;
3. Ñ: and then, on seeing the success of those whose benefit has been wished for and the removal of whose suffering has been wished for, they should be practiced as being glad—and gladness has the act of gladdening as its characteristic;
4. Ñ: but after that, there is nothing to be done and so they should be practiced as the neutral aspect, in other words, the state of an onlooker—and equanimity has the promotion of the aspect of neutrality as its characteristic;

Ñ: therefore, since their respective aims are the aspect of benefit, etc., their order should be understood to correspond, with loving kindness stated first, then compassion, gladness, and equanimity.

"We are all one" is not Buddhism

No, that's not the theravāda point of view. That's a fallacy or wrong view called, "He assumes consciousness to be the self", in twenty self-indentification-views.
Each arising aggregate is different from the other aggregates, different from e.g. other people's aggregates, past aggregates, far aggregates.
They all are the aggregates, but no one is the same.
Although there is a conditional relation which is called "Decisive Support" i.e. upanissaya (or in this clip that's translated as "Powerful Dependence"), so that past consciousness is a Decisive Support condition of present consciousness, but that is not the same as saying that the past consciousness "is" the present consciousness (i.e. the consciousness which it affects in the present).
Preceding states are related to subsequent states by the "Decisive Support" condition.
The aggregate is the Conditional Relation and Dependent Origination. Every relation has more than one cause and more than one effect, so don't find "the one" in Buddhism because it's self view.

Monk's Vinaya is not SīlabbataUpādāna

What comes with a set relates to the other members. Sīlabbata can't come alone, so it's meaning already came in its context.
Depentent origination means aggregates' relation.
Taṇhā means craving, addict.
Upādāna means caving again and again.
Diṭṭhi means the mental habit of the misunderstanding in the aggregates' relation.
DiṭṭhiUpādāna means caving again and again of the misunderstanding in the aggregates' relation. This is only unwholesome.
Sīlabbata means doing verbal and physical habit, depending on Diṭṭhi. This is able to arise with wholesome, unwholesome, and neither wholesome nor unwholesome, e.g. the thinking "I want to be a Deva in heaven" is arising with SakkāyaDiṭṭhi (unwholesome) but next moment the doing giving a gift, follow that SakkāyaDiṭṭhi for going to heaven, is arising with wholesome.
SīlabbataUpādāna means caving again and again of doing verbal and physical habit, depending on Diṭṭhi.
See DN MahāNidānaSutta:

So it is, Ānanda, that feeling is a cause of craving. Craving is a cause of seeking. Seeking is a cause of gaining material possessions. Gaining material possessions is a cause of assessing. Assessing is a cause of desire and lust. Desire and lust is a cause of attachment. Attachment is a cause of possessiveness. Possessiveness is a cause of stinginess. Stinginess is a cause of safeguarding.
Owing to safeguarding, many bad, unskillful things come to be: taking up the rod and the sword, quarrels, arguments, and fights, accusations, divisive speech, and lies.

The Answers

What does this fetter really refer to?

It refers to SīlabbataUpādāna.

Is it clinging to rites & rituals and thinking that these practises by their own can lead to liberation OR does it refer to clinging to precepts?

It addicts to do follow to DiṭṭhiUpādāna again and again. So if the rites, rituals, practises, and precepts depending on DiṭṭhiUpādāna, it is SīlabbataUpādāna.

So if most monks just follow rules and precepts because the Buddha said so (or they are deemed to be effective), then this is called Silabbata Parāmāsa?

The mong who keep on 91,805,036,000 vinaya rules follow to Buddha because they trust the Buddha, who rightly understanding in the aggregates' relation, is not SīlabbataUpādāna. It is similar to when you are following an expert guide and you are going to arrive the right destination surely, no one can't say "you are going the wrong way" although you do not understand the map by yourself at first.
91,805,036,000 vinaya rules are keeping Tipitaka go on through 5,000 years, but some lazy buddhist people try to cut them off, while there are many monks still can do follow to all those rules. It is superficial thinking and killing Buddhism age because Theravāda Tipitaka still available nowadays by the Tipitaka Memorizer who did follow all those vinaya rules. And it is going like this until 5,000 years. The similitude is the chemist who has recited, memorized, and learned about the periodic table and the formulas from the past chemist generation to generation.
There were many Nikāya tried to cut some part of Tipitaka off, and now their canons already disappeared, right?

If it is the former, then most "rational" inclined people should have little to none of this fetter, no?
If it's the latter, then it's NOT about blindly believing a precept, but questioning it and seeing for oneself that it's helpful.

All ordinary people have SīlabbataUpādāna because they have DiṭṭhiUpādāna. They still have the mental habit of the misunderstanding in the aggregates' relation, DiṭṭhiUpādāna, so they still act follow to that habit, SīlabbataUpādāna.

However, it appears to me that many rules in the vinyana are there to avoid social faux pax and unnecessary conflicts. If we take the not-eating-after-noon precept, we will see that the Buddha has reason for devising such precept; but do those reasons still hold true nowadays? I doubt it.

It may be not important for 21th century, but it may be important for 22th century. The Buddhist age is for 5,000 years, not only for 100 years. Tipitaka should lose after Buddha's death for 1-200 years without 91,805,036,000 Vinaya rules, but it still going on because of the Vinaya rules. Who can understand entire chemist canons without the chemist expert, right?
By my experience with Burmese monks (stickest on rules), Thai monks (sticker), and the westerner monks (not stick), the Burmese monks can understand the whole Pali Canon deeply, while the Thai and westerner monks often distort the Pali Canon by their own opinion then say "Pali Canon is conflicting with each other". For example, the fabrication of MN 44 is talking about Jhāna, and SN 12.2 is talking about Vipassanā by each Sutta's context. But the Thai and the westerner monks mix them together then say "they are conflicting with each other." It is like that because many, almost all, Thai and the westerner monks are lazy to recite and memorize Tipitaka follow to Vinaya rules "the monk can't live without Tipitaka Memorizer Teacher if he has not enough Tipitaka memory, and it is counted as a defense each date, 10 dates 10 offenses."
I understand Tipitaka without cutting any part of Tipitaka off because I always support the monks who doing follow entire Vinaya rules.
How can one understand the action and its effects when one never do follow them all?

Iriyāpatha and sampajañña

1. It's the outspoken translation. Nothing is wrong by the context. See Ruben's answer.
2. However, the obvious serious wrong is the vocabulary translation. Pajānāti means "comprehension", it doesn't means "know".

Furthermore, when a mendicant is walking they know comprehension: ‘I am walking.’
Puna caparaṃ, bhikkhave, bhikkhu gacchanto vā ‘gacchāmī’ti pajānāti

3. The Atthakathā explains the comprehension, Sampajañña, to four here. These four comprehensions have two levels:
   3.1. The samatha level in MN KāyagatāsatiSutta which taught to the beginner, neyya. The listeners in this Sutta are the newbies, so the Sutta's structure point to Jhāna, CittaVisuddhi, at the end of each section.
   The practitioner begins by ĀnāpanassatiJhāna in sitting meditation, and keep to meditate Ānāpānassati in Section on postures and Section on sampajañña. This is the basis.
   3.2. The vipassana level in MN MahāsitipaṭṭhānaSutta which taught to the high level vipassanā practitioners, ugghaṭitaññū, in Kuru Kingdom. All of the listeners in this Sutta already practiced these 21 sections, but the end of each section, samudayavayadhammānupassivā dhammasamiṃ Viharati (the practitioner comprehensions the origin and the cessation in all practiced practices and the comprehending mind), is their last lesson of the practice, so MahāAtthakatha said many listeners enlightened as Arahanta after the listening.
   This level appeared in explained in MN MahāsitipaṭṭhānaSutta's Atthakathā. It's not for the beginner. If the beginner start from this explanation, he is going to stick at the 10 imperfections/defilements of insight, Vipassanūpakkilesa. This explanation is very popular however most of teachers, today, give it the the improper practitioners.
   That's why most of them can't enlighten in seven years according to the end of this Sutta. The sequence level is very important, when the practitioner cross the sequence, it means the defilements of insight still remain.
   The question owner creates this question because he thinks follow to this level.
4. the meaning of the comprehends is the same as above wiki link, except the fourth.
   4.1. The sampajañña of samatha level is...
   

   when a mendicant is walking they comprehends: ‘I am walking for the purpose, suitability, and domain of the non-delusion in the breath meditation’.

   4.2 The sampajañña of vipassanā level is...
   

   when a mendicant is walking they comprehends: ‘I am walking for the purpose, suitability, and domain of the non-delusion in the aggregates in the Dependent Origination cycle’.

   4.3 How can I know that explanation?
   I understand it from Sutta context after I recited and memorized MahāsatipaṭṭhānaSutta Pali for ten years (so I often tell you all to memorize the pāli to study Sutta). The context is already arranged from the basic to the advance like in the explanation in Netti.
   Pajānāti has already appeared before the Section on postures in the summary Section of this sutta, Ānapanassati Section, and almost all other Sections as well. It means the Section on postures must translate with those all sections as I translated above.
   So, what is written in wikipedia, it is wrong...
   

   While the nikayas do not The Sutta has already elaborated on what the Buddha meant by sampajañña as "the keeping comprehension of current meditation in four main postures and seven sub-postures", the Pali commentaries analyze explain it further in terms of four contexts for one's comprehension

   Actually, pajānāti and sampajañña is already elaborated in Sutta's context clearly already.

Avoiding ignorant, immoral people as much as possible is not opposed to loving-kindness

The Buddha repeatedly said to avoid ignorant, immoral people as much as possible, but isn't this - at least a little - opposed to kindness? I associate kindness with being benevolent, caring & somewhat open. Am I missing here something?

No, they have nothing be opposed to each other. Actually, they support each other.
The practitioner can do metta to every person, including the immoral people, every time because Metta is mental meditation, but the practitioner shouldn't be very familiar with them because the practitioner can derive their bad behavior.
We help and support a cat, e.g. giving food, but we shouldn't be very familiar with a cat because the cat can't teach us the four noble truth.
Avoiding the ignorant person is not worry or scary. it is understanding of the effects of each fellowship.
The practitioner still wants to give happiness to the ignorant person every time, but the practitioner is just careful to keep the distance between practitioner-self and the ignorant person.

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Metta is wishing to give happiness to the other living life(s).
What is that life?
The life is the aggregates in dependent origination cycle, so sometimes life has a wholesome mind and it's mental&physical factors, but sometimes life has an unwholesome mind.
Metta-mind doesn't care about life's mental state. Metta-mind cares about the entire of which is called "living life".
Mind that voiding from ignorant, immoral people is focusing at the mental state. We don't want to derive any bad habit from the ignorant, immoral people, so we should avoid being close with them.
For the example:
I have the only mother, so I can do everything to make her happy, but I have to avoid to study chemistry with her because she is ignorant of it.
I give some food to the immoral victims because I am so sorry with their suffering however I do not support their previous immoral and bad behavior. I am not going to be immoral and to have bad behavior like them.