1. I don't know a Death Knight well enough to comment. You could try a site like www.talentchic.com, for the most popular (talents, glyphs, enchants, gems) for each spec of every class. Not saying the top Unholy PvE build is an AoE/Boosting build, but whether Blood or Unholy you have the most popular builds based on parsing the armory.

2. You can send yourself RAF invites. I believe you can have 5 out at once, per account. And as the invites are used, you can send more out. I would personally put each wow on its own Battle.Net account. Which is a bonus if you are going to use an authenticator (definitely get a single authenticator or the iphone application, and use it for all your accounts). If you put the accounts on a single B.Net, they will be easier to manage, if you spread them across 5 B.Nets, you can log them in simultaneously with one code instead of across 3 minutes.

3. Not sure mistakes exactly. Everything I leveled were classes I considered as fun options. I leveled Priests and Hunters, which I did not end up playing past 60th; although both seem like they could be fun down the road. I did not level Warlocks or a melee team, and am in the process of 4x Warlock + 1x Priest (my only horde team) and am considering a melee team strongly. Pretty much, not leveling as many teams for multiple options during RAF was my "mistake" if you call it that. I did Shammies, Druids, Priests, Hunters. Did not do a Melee team (and 2-3 are interesting now), Mages or Warlocks. And I quit RAF leveling with a little over 6 weeks remaining (started on 60+ levels).