Been working on a DIY box for NAS using small form factor parts as a system to backup files from a home network of 5-6 PCs and laptops. FreeNAS or unRAID looks like the best way to go since I will use it mainly as a drive pool for incremental backup of the other PCs. I will not use it as a media/HTPC other than for my digital music library which I've been wanting to fully digitize from all my old CD's.
Update Feb 2018: The system is complete and I installed a trial run of unRAID which was easy to setup and configure. I'll probably stay with it for my storage purposes. I designated the 4TB N300 Toshiba drive as the parity drive and the Crucial SSD as the cache. I established network shared directories for music, family photos, home videos, incremental file history backups etc. to consolidate it all from the other PCs of my family members. It currently has 12TB of usable storage and can go up to 16TB later with the 4TB parity drive since unRAID requires data drives to be same size or lower than the parity. So far it is running well and it came together without any issues. The availability of ECC UDIMM memory was limited and pricey but I wanted a motherboard/RAM/CPU combo with server grade options. Although unRAID does not require high hardware requirements I may try other server OS programs later. Now onto to ripping all my CD's into FLAC and trying out Plex for streaming music!
June 2018 Update: This NAS build has worked out very well and been running smoothly since Feb. The InWin case is great to work with and I like the various server features it has like the slide-out motherboard tray and the LAN 1 & 2 and failure warning LEDs on the case. It was trial and error trying to figure which wires go to the correct LED pin-outs on ASRock motherboard but other than that it all went together nicely. The unRAID OS install was easy and I've set up my shared drives for incremental back-ups and archiving my media. Just finished ripping all my CD's to FLAC and using Foobar2000 as my music file manager. I did install Plex but have not quite figured out the software settings for my unRAID setup yet.