This build replaced a test 'beater' unit: I-4, 1.7Ghz, 4Gb memory, 2-240Gb HD, mongo Dell tower with ancient motherboard. Initial problem was two problematic ASRock Z170M Pro4S LGA 1151 Intel Z170 boards. Switched to an ASRock Z170M Extreme4 LGA 1151 board with no problems. Good to live close to MicroCenter. A-data memory was an introductory sale price. Processor may be overkill but why not at that price. Two 1-Tb hard drive were bought on sale. For the case I caved and went for a little 'bling' vs usual penchant of 'plain jane black'. DYI micro case works fine but probably not for first time builder. USB stick was MC check-out selection. PSU was leftover from another build.
Installed FreeNas 9.3-64 bit operating system using the Zetabyte file system. System is up and running flawlessly. With only two drives the system is essentially a Raid 0 Configuration(mirrow). Streams music and shares photos via wireless and direct ethernet via a Netgear G108 switch. Next project is to stream my VDI files for VirtualBox.
Curiosity got me to test overclocking of the of the I-6100 processor by 10% with success. Use Logitech wireless mouse/keyboard combo and ancient flat screen monitor. Once up and running the system can run "headless".
I understand that a 'real' NAS should use 3 or more drive and those built for NAS use.