(Help) First Gaming Rig

Hello,
I'm somewhat new here and I've read a few post about people and there setups. This question has probably been asked a lot but I need insight on my Gaming Rig I'm going to build.

Price Range: $500-$900 (I have a monitor, Keyboard, and mouse.

Use (Greatest to Least):Gaming (WoW, Starcaft 2, Diablo 3, Fallout NV, etc),Youtube (would love to see videos High res),Music, Web Browising, and Email

CPU: Intel Core i5 2500k Sandy Bridge (This is changible on what ever might be a better choice depending on budget, etc)

GPU: XFX HD-583X-ZAFV Radeon HD 5830 (Again like the Cpu changeable depending on budget)

Mobo: MSI P67A-GD55 (B3) LGA 1155 Intel P67 SATA 6Gb/s USB 3.0 (Dependent on Cpu)

RAM: MSI P67A-GD55 (B3) LGA 1155 Intel P67 SATA 6Gb/s USB 3.0

PSU:CORSAIR HX Series CMPSU-750HX 750W

Case:COOLER MASTER Storm Scout SGC-2000-KKN1-GP

HDD: SAMSUNG Spinpoint F3 HD502HJ 500GB 7200 RPM

That Averages out to $800. The OS will be Windows 7 Home OEM. Please Tell me if this is a good setup and if I can change anything so the cost can be...better on my Mom's Wallet  . Also I Forgot to mention I might consider running dual screens so please give me your 2 cents on that if possible.