A NAS is a good idea - lower power and less noise in a smaller footprint than a server - mine lives under the TV in the living room.
I'll recommend QNAP because that's what I have and it works well ( 219PII with 2 hard drives in it ). Synology also seem to be good from reputation.
Whatever solution you find, ask this question - what happens when ( not if ) a hard drive fails ?
An external drive kept off site with a copy of your films/data might be a good idea*, RAID will help, but isn't a full solution**. I keep a 2nd NAS in another physical location that syncs with my home machine automatically***.
* You will need to bring it on site to backup your collection as it changes though
** especially if the machine dies/gets stolen/flooded/eaten by the cat
*** so that it'll copy new stuff, but not delete anything already present