*FIRST PC BUILD* NEED ADVICE

Hey guys,

This will be my first attempt to put together a pc from scratch. I have been contemplating whether to buy a  gaming computer or to build one my self. Even though I have never built my own, I am willing to try. It seems fairly straight forward. The main reason for this build is gaming, particularly for DIABLO 3 and maybe 1 other game, but mainly just D3. My budget is between 800-1000 dollars. My expectations are for the computer to be really fast and for the game to have great graphics.I have already done some research on some parts at newegg.com and have came up with i think are some decent parts. Here is what I have so far for the main components of the build, please let me know what you think about the parts listed:

Motherboard: Asus P8Z68 V PRO/GEN3

Case: Cooler Master HAF 912

Processor: Intel Core I5-2500 3.3GHz or AMD FX-6100 3.3Ghz (way cheaper)

Memory: Corsair Vengence 8GB DDR3

PSU: Corsair TX-750W (is this the right amount of wattage? more or less?)

Graphic Card: HIS Ice Q X Turbo Radeon Hd 6950 2GB
                                           or             (These good brands? whats better?)
                     HIS Ice Q X Radeon HD 6790 1 GB

SSD: Crucial M4 128GB SATA 3 MLL
                               or         ( Do I need 128GB?)
           Crucial M4 68GB SATA 3 MLL

That about does it for main components besides the optical drive and the operating system. Let me know what you guys think. Please let me know if you think some brands are more reliable than others. Also I'm still really confused about the boot up process. Whats overclocking? and whats the first thing I should do when I fire up my build for the first time. Whats updating the drivers mean?..Any information will be extremely helpful to me. Thanks very much. Its greatly appreciated.