Actually, certain AM3 boards support FX chips with a bios update. Foxconn doesn't though, probably because it's an OEM board.
Yea the 1090t is a good CPU, but it won't work in that board either. 95w limit.
AMD Six-Core CPU Support:
* Phenom II X6 1065T 2900MHz – 95W
* Phenom II X6 1055T 2800Mhz – 95W
* Phenom II X6 1045T 2700Mhz – 95W
* Phenom II X6 1035T 2600Mhz – 95W
Yes, but that's a pretty penny for an older CPU. I would get the above mentioned stuff to see if it gives him the increase he wants before dropping that cash on the processor.
Nothing. Get whatever is cheapest. Your dad I assume doesn't game on this PC and the software to what I'm to understand isn't GPGPU capable so it won't help anything.