1. Up to you.
2. 5970 is the antithesis of quiet. It is brutally loud. It also generates immense heat. 2 going at full bore will easily increase the temp in your office by 10-20 degrees. Only option is watercooling or accelero 5970 (if you can find one).
3. One, yes. Two 5970s, not reliably.
Thanks. Yeah, I was worried about the noise and the heat.

What if I were to switch to a different GPU? Are there any options out there that would work with the above setup and possibly not make my office a sauna?
I could go up to the COOLER MASTER Silent Pro Gold Series RSA00-80GAD3-US 1000W for the PSU, but it's $199. Any decent 1000W options between the one listed above and this one? $135 is quite the price jump...
I may just have to bite the bullet and have it at the house.