I want to build a home media server for my home network. I want the ability to stream DVDs, music, photos to various clients in my house. The clients include: xbox, roku box, win7 laptop, imac, ipad. Might need to stream to 2-3 clients simultaneously. Since I have a variety of clients, I put together a list of components so far that can handle on the fly transcoding. I reaize my list of parts is overkill otherwise. My other requirement for the server is that it be a mini-itx form factor. I want a smaller unit so that I can place it in my entertainment center connected to by main HDTV and my Asus RT-N56U router which is there. I want to start with 6TB of storage with the ability to add more down the road. I think I may run this machine as a PLEX server to handle the variety of clients I have. I am intrigued with putting Ubuntu on the machine as oppose to Win7 or Win8 in order to save some money on the OS.
I originally was leaning towards a synology ds413 NAS instead of building a unit but I learned that they are not adequate to do transcoding if that is needed. My budget is around $800.
You could opt for a lower-power PSU and save a few bucks on it. Seasonic is a great brand, but even 550W is overkill for a machine with no GPU.
Also, 6TB is a lot of data to lose if you're running a striped RAID and it fails. You might be better of looking at 3x2TB drives and a RAID 5 or such (really depends on how worried you are of drive failure, and if you would rather wait and add redundancies later down the road.
Finally, you might like FreeNAS for an operating system, it's basically built for this type of thing.