I'm a big proponent of ATI GPUs for gaming but if your interest is in Folding@Home then I would suggest maybe a 3 slot Nvidia 780a based motherboard with three 9600GTs or something similar folding for you. You'll get more PPD. I don't know about the stability of Nvidia's chipset business though so that may be risky. I sure wish F@H had optimized the code for ATI GPUs FIRST rather than throwing their resources at CUDA. CUDA gets the job done though so I can't knock 'em for that.

Also since you're going to take the time to build an AMD system, the SB750 motherboards are supposed to be out August 6th. You may want to wait until next Monday to make a solid decision.

Now to actually answer your questions.
1) Make sure you have a strong PSU to drive 2+ GPUs plus an overclocked CPU and motherboard.
2) High end air cooling will allow 3.2Ghz on a Phenom, especially if you have an SB750 backing your overclocking endeavors.
3) That ram will get the job done for overclocking. DDR2-1066 is better but oh well, you already have 8GB of high quality DDR2-800!!!

I've yet to see any overclocking on that Phenom 9350e except for a Tweaktown review....(http://www.tweaktown.com/reviews/152...ore/index.html) and I don't trust Tweaktown all that much. The 9350e is 2.0Ghz though so it'll probably get the job done. Price wise though, may as well look at higher clocked Phenoms like 9550 or 9650s.