1. Dark Irons DO use taboo magic, they're the Dwarf Warlock trainers and such remember?
I know, but Demonic practice doesn't appear to be foremost to their culture and society. Honestly, it's not very defined beyond darker magics. Shadow magic, some demonic stuff, taboo shamanistic stuff, etc...
2. I fully support some of the Tauren old concept stuff being brought in.
If its done right. It'd be interesting if some of the Tribes had class-related specializations. Bloodhoof might have been the Warriors, Runetotems the Druids, etc... Grimtotem the Mages.
3. It just feels weird for me that the Blood Elves would get hurt by Garithos and then run back to the Alliance's open arms not so long afterwards.
Well, if you take it from the context of the end of the mission they fled to Outland, I'd agree, but after seeing where Illidan's leadership took the Blood Elves, how he himself fell despite the power he held, etc... If the Blood Elves reflected upon all of this, and then received a friendly ambassador from Stormwind, Ironforge, and Gnomeregan, it doesn't seem odd at all.
Personally, I'd rather have seen that happen and the issue of Garrithos answered once and for all, that to the remaining Alliance's knowledge he never held a position higher than Captain of a single Garrison of Lordaeron, and took up the title and rank of Grand Marshal without any knowledge of the rest of the Alliance, in the hopes of, after successfully reclaiming Lordaeron, being named its Regent.
Perhaps the actions of Garrithos would even be a catalyst to force the remainder of the Alliance to accept the Blood Elves renewed membership. They were mistreated by a man who misrepresented the Alliance. Old allies deserve better respect, and despite their darker path, the Alliance intends to make up for this with what aid it can.