The only limitation is that for any badass normal type, they should specialize in being really good at a few areas and just being competent at others. I basically don't want scientists that are masters of every discipline or batman-types who are good at everything. And their mastery of their skills and background have to be plausible. Because when you come down to it Batman's backstory isn't very plausible. And any scientific technobabble has to sound plausible at least too. 

EDIT: Huh, you had political turmoil too?

And it should be noted that the PCs can be more than just villain ass-kickers. They can be medical specialists, tech guys, investigators, etc etc.