Budget home made build

Hi I'm new here and I'm looking forward to build my first NAS Build.

I'm planning on a 2 X 4 TB WD reds in raid 1 and a 128 gb SSD.

The build is for a home server to store my movies and RAW pictures.

I want to access it on the go 24/7.

I was thinking of using a used parts.

Cpu: Xeon E5 - what model should I get
Motherboard - what should I get?
RAM - how many?