Just a though, but i'd avoid the core editions, the cooling is inadequate and very loud under load. The warranty reflects this as well, get the Double D versions if you can to get better cooling and the lifetime warranty (if they still offer that).
To answer your specific questions, i believe you are supposed to be able to use up to 4 in crossfire, though it's anyone's guess how well that would actually work, and it would be hard to find a mobo to do it with. You should have something like a 750w bare minimum for two of those with an 8350, though i'd probably get an 850 to leave some breathing room.