Game development

performance betweene using xna and dx?

can you use c++ and dx to make games for xbox?

what do you have to do to sell a game for xbox (via xbox live)? I heard about some membership that cost 100$ that but i am not sure. 
how good does the game have to be to actually earn some money(example)?

what about selling games for windows? is the easiest way through some sites? how good do they have to be to earn some money?


I made some games with c++, and some with python, I am learning c# because I want to earn some money making games or business apps. But should I go back to c++ because of speed?


thanks