Home server for downloading, sharing and steaming large files

Hi guys
My brothers and I are thinking of building our own home server for downloading, sharing and steaming large multimedia bittorrent files such as dvd ISO and hi-def movie file. We usually leave our computers on all day and sometimes end up downloading the samething on the internet. We are thinking that having a server might help reduce our electric and internet bills. The machine will likely be on 24/7, so we are looking for a build that has good power efficiency but also has enough juice to simultaneously download and steam multiple contents (in case we decide to watch movie from different locations of the house at the same time). We try to limit our budget around 500-600 usd for case motherboard cpu and ram excluding the hard drives. Any suggestion is greatly appreciated.

i3-2100, motherboard of your choice, 8gb of ram, 400w psu, etc.

asrock z68 extreme 3 gen 3.

Corsair cx500w

Antec Solo II or fractal design define r3, both are excellent cases for quietness. You might also want to add an ssd to the build.