Instead of building a power sucking monster to act as a server, might look at a NAS. Most now even have security camera software and built in iTunes servers.
For my family I run a 5 drive NAS box with five 1TB drives in RAID5. Serves as a central media storage and desktop backup for the house.
For a backup routine, when I rip/convert my movies I burn the converted mp4 off to a DVD when I get enough to fill it. Usually 3 or 4 movies. Then add that to a spindle that sits in the corner for rebuilding if for some reason the NAS eats its own head. More sensitive/non replaceable stuff like the taxes and family photos, have an external drive that I mirror the data to regularly that gets stored in a safe.
Best part, most NAS boxes under heavy load pull less wattage than a 60w light bulb, and is the size of a shoe box.
I have used Buffalo, Thecus, Qnap, and WD NAS boxes. Qnap hands down is the best interface I have used, also very nice,quiet, well built units. I currently run a Thecus unit at home, but think my Christmas gift to myself will be a Qnap TS-569L link