i have done a simple little build
-i3-4130 3.4GHz Dual-Core Processor
I have checked on plex forum, people were using ivy i3 and transcoding on the fly 1080p
-1150 mobo, since Haswell is new, we don't have a lot of info on these motherboard, but i trust gigabyte from my experience.
-hard drive : I don't know if you are going to hardware raid/software raid them if you aren't then you can buy bigger drive like this Toshiba DT01ACA300 (3tb) 130$ x3 to get 9tb
for the linux os you can use a usb key.
First thing I learn during my time on this forum, raid is not equal to a backup. So for important stuff it better to have a external hard driver, or use cloud. Raid will help you in case of disk failure. I suggest you to do it, in case one day one hard drive fail and you loose all your media that was on your disk. Using a cheap dell perc 5i/6 raid that you can find on ebay for 40-60$, you can have a simple raid 5 ( which with 5 hard drive of 2tb , will give you 8tb, ( raid calculator
For the stuff you want to do with your server : http://linuxhomeserverguide.com/
Very easy guide how to setup everything on linux.