That motherboard supports dual channel memory architecture, which is a technology that, in effect, doubles data transfer speeds of your RAM. However, to enable dual channel memory, you must install 2 sticks of RAM so I recommend you get 2 x 4Gb. And to ensure compatibility, make sure you get RAM that is listed, or RAM with the same specs as listed from the Memory Support lists for your motherboard
You do not have an operating system listed. With 8Gb of RAM, you will need a 64-bit OS so I recommend 64-bit Windows 7 or one of the free Linux alternatives.
You said you have a hard drive, do understand if you are planning on moving a hard drive from another computer, and that hard drive has Windows installed on it, it is most likely illegal to use that copy of Windows on this new machine (not to mention, Windows will probably choke when it discovers all sorts of new hardware first time you attempt to boot.
I also don't see a power supply. Don't try to cut budget corners with a cheap PSU. Get a good one that is 80 Plus certified from a good maker. I like Corsair and Antec PSUs.
The use of an aftermarket cooler on that AMD CPU voids the CPU warranty. Since the supplied cooler is an excellent cooler anyway, no problem.
Note you must have a DVD drive to install Windows 7 as it comes on a DVD, not CD.