Thanks - your advice was reassuring!
Yes I am using the Cooler Master Elite 350 (CMP350) and while it is a tight fit I think I am able to get (11) 3.5” HDD in there. Right now I have (2) 12TB and (2) 8TB all purchased when on sale.
The Arctic Freezer 12 is a bit loud but I suppose it’s only doing its job.
I stopped the fan alarm 
by going into BIOS and disabling BMC Alert Beep.
All my HDD are recognized after plugging them all into the SATA 1-5 ports, while I left the SATA 0 port open for an SSD which will arrive later. The SAS ports - how do I use these and plug in SATA HDD? I may have mistakenly assumed I could plug a normal HDD into the SAS port.
Fortunately, I did not have to flash the BIOS. RAM was NOT the issue and all 16GB are recognized. About to install UNRAID Plus (up to 12 drives). Fingers crossed 
