Is a 650 W power supply overkill for a 484 W max build?
That's pretty overkill. It might be better for you to get a 550W or a 750W. The 550 if you're trying to save on budget, and the 750 if you want the ability to SLI/crossfire two high end cards later.
Yes, but PSU's can span multiple builds. But as /u/WishIHadAComputer said, a 550/600W would function just as well.