About vampire PCs: well, Vampire Embrace and Vampire Hunger are pretty popular mods and allow you to talk to NPCs when you are a vampire.
And Vampiric Hunger adds an Illusion spell that "masks" your vampiric features; if you enable the option for MWSE, it will even restore you "normal" character face. Technically, it actually removes the vampire condition from the PC for as long as the spell is in effect; so this feature allows you to play like your character isn't a vampire at all.
This means that using this feature will allow the player to use your mod even if the PC is a vampire (actually, it makes a lot of sense that you have to use this special power to have six with someone! ).
The problem is that AD will not be playable by people who want to play a vampire character but doesn't use MWSE.
Anyway, I just thought you might like to have some feedback about this. Personally, I play with MWSE and VH, so I have no problem at all.