That CPU is fine for general media server duty but I would step up to at least a quad core i5 if you are going to be transcoding (with plex, airvideo, etc). Also, you won't get any stutters/freezes when you are streaming several sources and transcoding at the same time.
+1000 on using flexraid, especially for 8 drives or multiples of 8 drives. I have well over 20 drives and have never had a drive fail in my life, but it's great to know that I am covered (probably long overdue) and its easy to use.
I would also encourage you to consider splitting your drives into separate 8 bay enclosures vs putting them in your case. Makes it much easier to upgrade you pc server box without disassembling it to remove all your drives and easier to swap out a drive in case of drive failure.