I was uncertain it qualifies as SFF, but given a few here seem interested, will get to create a build thread. Curiously enough the drives cooling is great, when I encode it gets even better as the radiator fans ramp up (and they are not noisy actually) and more air gets sucked in on the front towards the back, I find the HDD cooling design is great.
The hdd cages have a 3pin fan connector each and you can have fans controlled based on HDD temps, you can also achieve that in the OS if you want, I personally have them fixed at 50% and then they ramp up based on CPU temp. By the way, my cpu never went over 75C average even during 2 days of straight 4K encoding with all cores loaded.
The OS I use is unRAID, you can check it out here:
https://unraid.net/