Payments are possible, I have a working version of credits for my game in progress but its not overly user friendly. So it is possible. Real time multiplayer requires a plugin ATM I believe. I'm using php and MySQl for my game which is pretty close to real time but there is a definite delay.
I'm more knowledgable with the Facebook platform so I can't speak really about real time multi. I'm sure someone else will chime in. For credits currently you will need php skills, and the browser standard plugin. I'm working on updating my Facebook plugin to include the javascript credits system but its probably a few weeks off. Until then browser redirects is the only solid way to implement credits.