How large of brakes can you put on a stock set-up? Can you only go up to 10", or can you go bigger?

I'm not sure about that. I know there's an 11" DRUM setup that you can use, but I don't know about the discs. If you do a search on some of the threads here, they will probably tell you what size those Cad rotors are, or the 4th generation Camaro rotor size.