Kell, I found creating the "rules" for the RH books VERY challenging. You want to give your vamps certain powers, but they can't be powerful enough to be able to zap all their enemies, or you won't be able to put the vamps in jeopardy.
Other than that, what you can do with your vamps is pretty unlimited. You're pretty much free to do what you want as long as you remain consistent and remember to actually follow your own rules. That's actually harder than it sounds. I can't ever remember if my vampires breath or have heartbeats!
I really like traditional vamps, so I borrowed from existing lore from everybody from Bram Stoker to Anne Rice. That is, they can't see their reflections, have to be invited in, that sort of thing. I was also a big Buffy fan and would love to eventually have a whole variety of demons like Joss Whedon did.