Man, a Buffy game. That takes me back. Used to play on the Buffy game set in Vegas back in the day. It was a headache, but good times.
A tip: the Buffyverse is basically a comic book universe and has an incredibly wide variety of character types (from the typical slayers, witches, vampires, and demons to robots, mutants, and super soldiers). If you've got a theme you want to explore, or character types you want to focus on, be clear about it.
Also, there is a high probability that a Buffy game will become very nearly exclusively gay. Dunno why. Saw it happen, though.