As far as time frame, etc, we're wanting to keep this rather simple to start out with. As such the events with Scarlet Witch and the Civil War have not happened. Nikita and I talked about the Civil War atleast, and we thought something with that much impact would be more interesting having PC's involved with it shaping out, than to expect people to know the complexities of the plot line and throw people into it.
As for what we are looking for in a character profile. A name, codename (if you want), write up of powers, physical description and a brief history would be good.
As for allowed characters, we are very open. I'll talk with Nikita about what we can mark the game as, since I think we would both enjoy seeing it broader than just the goings on of the School. After all, two characters we will likely have in the game are not mutants at all. Allowed characters are Marvel/DC heroes as well as original characters... from either setting. We will be having it in the Marvel Universe however, as the view on vigilantes is much more realistic, people reacting to mutants in a much more realistic way.