You're correct about the UD Eeveelutions, as I definately won't be running them in this deck. Funny thing is, I kinda had the idea to make this deck into a "poor mans Arceus" deck from the beginning. Obviously Arceus is better, but it also takes a lot more time and resources to master, which I currently don't have. So this will have to do for now.
As far as BTS goes, It's not COMPLETELY necessary. You just Undevelop, and re-evolve to a different Eevee that's already on the bench, provided you have one. Yes, BTS makes this so much easier, but I'm completely out of copies and some online retailers are selling them for as much as 12 bucks a piece! Needless to say I don't require them THAT badly.
I've got several copies of Umbreon MD already and will most likely run 2 Umbreon UD/1 Umbreon MD. Free retreat and no weak are definitely nice attributes to have! Also, I believe Espeon Prime is necessary so Donphan/Machamp don't completely Stolen/pillage/destroy this deck. Plus I'm going to run Rainbow especially for it and being able to hit Donphan/Scizor for a consistant 60 dmg(80 with belt) both bypassing Exoskeleton on Donphan, and Special {M} energy/resistance on Scizor are just too fun.
As far as Eevee's go, I run 2 MD and 2 RR. I believe that RR is much better due to the ability to grab the exact 2 Eeveelutions you need to counter whatever it is you're playing against. I run 2 MD because I'm not going to run Collector in this deck(again, no spare copies) and since Dual Ball is very flippy(my Collector substitute...not a very good one but yeah well you know....) I can't always rely on it getting my basics out.