20TB Rackmount Build, am I headed in the right direction?

I was asked to spec a 20TB FreeNAS RAID-Z2 system for work. It will be constantly backing up all kinds of data. Server backups, user data, website backups... I've read through the hardware recommendations, but I don't know much about this. Here is what I have so far.

Chassis: Supermicro 2U 560W
Motherboard:...

20TB Rackmount Build, am I headed in the right direction?