The mobo - http://www.asrock.com/mb/AMD/970%20Pro3/?cat=Specifications
- will take faster ram. I'd get at least 1600
You should be able to get a GTX760 cheaper than the HD7950
You should get a better power supply than the CX600. You'd only need 500W if you had a good one anyway. Try a Seasonic 520, XGX 550 or Antec HCG 520M
If you put more money into a motherboard, you wouldn't need a sound card. The ASRock 970 pro 3 is already OK.
Whichever motherboard you get, it'll already have an ethernet card and port so you won't need the adapter.