Firstly, I would heartily recommend the novella ‘Blood of the Highborne’, which is part of the anthology ‘Paragons’ It gives you a lot of info on Blood Elves, Liadrin being one of the protagonists of the story, going from Priestess to Blood Knight during it, as a major part of it happens during the Fall and immediately after it. It has pretty rich lore on Blood Knights and Farstriders alike.
The Light is a tricky one. I’m not about the M’uru thing, as everyone has already covered that, but we do know that Thalassian Elves could be Classical Paladin’s, who worship the Light in the same way as humans, One of Uther himself’s own pupils was such an Elf called Mehlar Dawnblade. Now given when Uther was knocking around, we know therefore that Quel’thalas had Paladins before the Blood Knights were even thought of Though Mehlar remained with his people and has since became a Blood Knight. What I’m getting at is that the concept of Paladins was known to the Elves -before- Blood Knights existed, and they likely worshipped the same was as Humans and Dwarves. Many, like Mehlar, (and Liadrin herself for that matter) utterly lost their Faith during the Fall.
Blood Knights would generally be well regarded these days, though it was not always thus, there was the famous rivalry with the Farstriders, who disagreed with the imprisonment of M’uru and the Blood Knights ways. Silvermoon shows us (Because the damned place is still stuck in eternal TBC) that the distaste was mutual. To a certain extent (even though I main one!) the Farstriders were being a little unfair, the Blood KNights did what they had to, to survive, whereas in canon lore it is stated that for some reason (Possibly the fact that they have vestigial traces of Nature Magic within them) the Farstriders were the most unaffected by the destruction of the original Sunwell out of all the Blood Elves.
As to how the rest of the Horde see them, I don’t think they would have any particular opinion either way, other than that they are one of the wings of the Blood Elven armies, and are Elite Heavy Cavalry. None of the Horde races bar one has ever had any negative experiences with them (They were not created in time to have fought Horde), and whilst Trolls and Elves sometimes have beef, the Darkspear have never fought the Blood Elves. The Trolls with the Horde at that time were Amani, the Darkspear weren’t even -in- the Horde yet, so they have only ever been allies. Now…the Zandalari……Yeah…that could well be a different story. The Zandalari just got their backsides handed to them by the Blood Elves a few years back, on the Isle of Thunder. Quite how that effects Zandalari opinions of Blood Elves remains to be seen, though there don’t seem to be any problems so far.
Blood Elves seem to very much understand the concept of Combined Arms warfare, forming battlegroups made up with the varying branches of their military. It seems highly likely that the old dislike between Farstrider and Blood Knight has been put to bed some years ago now, as the two types happily serve together in said battlegroups (The Sunsworn in WoD’s Draenor are a good example of what I mean).
The Blood Knights, like the Farstriders do indeed have their own particular style of military, theirs being much more based along proficiency with the Light, or so it sounds from their Titles.
Wowpedia gives a good idea of the ranks, and the source links to canon lore. As everyone knows, it starts with the lowest, Initiates, and ends with the Matriarch (theoretically Patriarch in the event of Liadrin’s demise)
Whilst the Blood Knights are very much a self contained military force, and Lor’themar Theron due to his bond with Liadrin regards her as his ‘Go to’ person when assigning commanders, her direct boss is Halduron. The Magisters aided in the creation of the Blood Knights, but the Blood Knights are Military, so fall under command of the head of the Thalassian Military, which is Ranger-General Halduron Brightwing.
Now contrary to how the Title sounds, this does not mean that the Blood Knights have a Farstrider boss. (I mean the current one is, but I’ll explain)
Ranger-General is simply the title given to the head of -all- Quel’thalas’ military assets. It is not solely a Farstrider Rank, because it predates the creation of the Farstrider order by at least a thousand years. It’s kind of the same as how Lor’themar Theron’s -military- rank is ‘Ranger Lord’, however he is now the absolute ruler of Quel’thalas, so…outranks Ranger Lords.
In the event that Halduron was killed, and Liadrin elevated to Commander of all Quel’thalas’ military, her rank would technically be Ranger-General, Even though she is sure no Ranger, whilst remaining Matriarch to the Blood Knights. This is of course assuming that Lor’themar doesn’t change the Title, I mean, he already changed how people become Ranger General, as it now seems to be on merit, rather than just passed down the Windrunner family line.
As for Guilds, I have only ever had amazing interaction with the folks in Division 23, and would heartily recommend them to anyone wanting to get into Blood Knight RP. They don’t tend to peruse the forums much, so your best avenue is probably a /who Division in game, but I assure you of their quality.
Other than that, Check out Aerilen’s guide as posted by Loras above, grab yourself a copy of ‘Paragons’ which features ‘Blood of the Highborne’(might be tricky to find, the only version I could find was in German, unless you -are- German, in which case that will be a doddle!),
But yeah, check out Aerilen’s guide, definitely.