I hope I'm the first to welcome you, but knowing the community I'm not! But just in case, Welcome to City of Heroes!
I'm going to be a bit vague for your first question, though I know opinions will differ as much as possible between people. There really isn't any power set, or combination of power sets, that are unplayable in the late game. Granted, you might be able to min / max in a bad way accidentally, but with the ability to preform a respec every 10 levels, think of it as more of a learning experience. Using respecs can allow you to play a little looser with your picks early on and live with some trial and error. You certainly won't be able to gimp yourself without intentionally trying to.
As for your second question, roleplaying is not required, or really catered too more then any other style of play (with the exception of PvP which was kind of tacked on). It might seem like RP has a pretty high standing here, but keep in mind this is a community of enfranchised players who have, for the most part, loved this game and the interactions within it for a long time. So really, don't worry about being judged by the RPers, they really are nice people, and every single one of them understands that not everyone does it.
Honestly, you'll never get banned for not RPing (even on the unofficial RP server), and making your Hero look however you like is a blessing you can enjoy (especially since I don't think Trademarks are being enforced. Right? Maybe?) no matter what group you're playing with. The best thing about this game has always been the community, and that is true of the RP community. I've never had anything but positive experiences with them, and hope you get to experience similar interactions!
And once again, Welcome!