You can have as many characters as you like, but I would reccomend not going overboard and making 100 differnet ones. 3-5 should be ok
Another thing is that I think that we should have 1 ability in this world. Apart from the shows characters of course. And also, I think that we should not allow EM and IA apart from Sylar. I think that AR should be ok because you only have one at a time. This will make it easier and more interesting in fights instead of having like 4 powers, your characters will have to use strategy.
Please say here if you would like 1 power or multiple (I strongly reccomend 1) and then when the decision is made I'll put the RP thread up