So this is only a server? its not going to play movies just store them to play on another device? Is it going to play games or anything that is cpu heavy?
This is a fast system that is budget orientated. For a server or HTPC type build you don't need anything more than a dual core cpu. This MB has HDMI on it already and can act as a HTPC as well (depends on what software you use). G.skill RAM is very good and there are deals where you can get 8gigs for $30, but you just have to wait for them, the RAM I selected is very good. Do get more than 8GB, its a total waste for 99% of users. This is an AMD system as you wanted. You don't need a high power PSU but one that is efficient and has lots of SATA connections, so the Corsair HX750 fit the bill with 12 sata connectors. There is no need for a video card, video is built into the CPU (APU) and the MB has HDMI output as well as DVI.
ASRock A75 EXTREME6 FM1 AMD A75 (Hudson D3) HDMI SATA 6Gb/s USB 3.0 ATX AMD Motherboard with UEFI BIOS
AMD A4-3400 Llano 2.7GHz Socket FM1 65W Dual-Core Desktop APU with DirectX 11 Graphic AMD Radeon HD 6410D AD3400OJGXBOX
G.SKILL Ripjaws X Series 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10666) Desktop Memory Model F3-10666CL7D-8GBXH
CORSAIR Professional Series HX750 (CMPSU-750HX) 750W ATX12V 2.3 / EPS12V 2.91 SLI Ready CrossFire Ready 80 PLUS SILVER Certified Modular Active PFC Power Supply
Totals $358 with a $20 rebate.
When getting the HDD's I would suggest going with the new 3TB HDD's that are only 3 platters. The prices are not that bad right now but they should drop as soon as production ramps up again. I'm presonally looking at the Seagate 3TB, but it looks like the price is all over the place, it was $150 recently.