I have a few questions if you don't mind.

Did you use the SSD because you had it laying around or you actually had a reason for it? Same question for the 8GB ram.

I was thinking of building something similar to you, and am very interested in keeping everything to the lowest power usage with exception of the GPU's, in short, cpu/mb/mem heat/power usage to the lowest possible.

Also what PCI you're using on your rack? Would you have a link from where you got those from and their price at the time?

And good luck on your build!