Yeah, no. I'll give you props for being so hung up on Superman, an afterthought example in my proposal. Flash is essentially limitless, and it wouldn't take much for an RPer to bring out massive asspulls to godmode, villain or hero. Hell, even Firestorm is freaking OP. What you see in the games and comics happen only because of the game limitations or plot armor. With RP there would be no limits. For this to work, you'd have to have fair players to work with the OP characters, and a fair and just GM to bring balance. 

But yeah, I don't know shit about RPing since I'm a novice. I do believe this won't work out at, least for me so I'm out. Good luck with the stuff.