The higher RAM is for overclocking your processor. Coolbits overclocks your graphics card (quite nicely I might add).
The 3200+ Athlon 64 is the equivalent of "hyper-threading" for P4s. I'm not going to get technical or anything but trust me, that processor will do very nice with games.
Get Lasereth or someone to explain it in excruciating detail
I'd get an Enermax PSU if I were you. You are going to have some damn-nice parts in this puppy, so I'd get a damn-nice PSU with it. That's not to say the one you chose isn't awesome, but I wouldn't be so sure of the performance when compared to a high-end PSU such as Enermax.