I'm asking this for RP reasons for Skyrim's DLC of Dawnguard. I've looked high and low into Vampirism lore in TES, and the only things I can find is that there are creation of and part of the sphere of Molag Bal. My questions are:

• Was there an original race that Vampirism affected?
  
• Is there any race that "Accepts" Vampirism?
  
• Is there any race that particularly benefits more from Vampirism?

The third one, and this is the only one I can sort of answer would be the Dunmer because of their resistance to Fire would negate, at least up to Stage 2 the weakness to fire that comes with Vampirism. Of course lore-wise, are you still a Dunmer once you're a Vampire, or are you just a Vampire with a Dunmer-like appearance?