How much need for future expandability to the NAS do you foresee? Will you need to add space to the initial RAID set you configure or will your initial sizing be enough for the lifespan of the device?
I'd personally look at
FreeNAS, it'll do what is sounds like you're after and can run on pretty much any old hardware you have lying around. If you're looking for a good case for a home built NAS, check out the
Fractal Design R2. 8 3.5" drive bays plus 2 5.25" bays, fully sound insulated. Amazing case, just picked one up last night for my movie/tv NAS at home.