Building a small server thing

I really didn't know whether to post this here or on the Enterprise Gear, but anyways I am trying to build a server with some really cheap stuff online.

The CPU I chose will be 2 Opteron 6172's because they seem to be dirt cheap on ebay.

The Mother Board will be a dell Power Edge C6145

I will have 4GB out ECC DDR3 for now

Can someone help me figure out how PSU's for servers work and a good place to get one
Also recommend a Enclosure
Also what OS?

I plan to be rendering videos in blender and it takes a metric shit ton of time.