1) What are the best Vampire mods out there? Also, are there any mods that make bottles of blood usable for vampires, and is there a mod that lets you make these?
In my biased opinion, the best vampire mod is http://www.gamesas.com/index.php?/topic/1197105-relz-blood-is-everything-classic/, which I just released a new version of yesterday. I chose not to recognize bottled blood, but BIE completely reworks your relationship to blood and feeding on it, so they're not really necessary. (Need blood? Just kill something and drink from the body!)
http://www.tesnexus.com/downloads/file.php?id=37088 has recently added support for vampires collecting and drinking blood from corpses as well, but I'm pretty sure that it only satisfies that mod's "thirst" need and does not affect the progression of vanilla vampirism (and probably doesn't affect any modded versions of vampirism either). A search on TESNexus should turn up a couple mods that make blood bottles usable by vanilla vampires, but you'd probably be better off selecting a vampirism mod first, then looking at options specific to that mod for getting bottles to behave the way you want them to.
2) What are the best companion mods out there?
http://www.tesnexus.com/downloads/file.php?id=28977 is very good and extremely popular. I've seen a lot of people saying she's the best (and very few saying otherwise, unless they're complaining about the absence of explicit "romance" options), although I haven't used enough other companion mods in Oblivion to know that myself - once I tried Vilja, I stopped looking at others.