sybreeder

+1 I also use ikea rack The best part is that you can stack them however you want. 

Hm From what i understand you want to use solution like unraid and windows machine that was presented on the LTT YT ? 7GPUs and sth like that ?
ESXi can do that and basic version is free. You can create 2 VMs - 1 for freenas, second for windows 7. Then passthrough GPU, USB, etc for win7 and HBA for Freenas. It should work. But it can be problematic. And that server needs to support VT-D

Forget about RAID 5. Go with Raid 6 or RAID-Z2 if you'd like to use FreeNAS. In case of 4TB disk risk of array fail when you lose 1 drive is very high. 
BTW Freenas is great for there kind of storage. 

It only works for straight backplanes, where every lane of the SFF connector goes directly to a drive. Anything with an expander I'm pretty sure wouldn't work.

+1 I also use ikea rack The best part is that you can stack them however you want. 

I have something perfect for you then.

We used this in the offices before for really large video files  It works like Dropbox/Google Drive. Only limit is your local machine. You can setup your separate machine to run btsync and he can do the same for you and your partners pc 

https://www.getsync.com/

+1 I also use ikea rack The best part is that you can stack them however you want.