DIY DAS

I'm putting together a motherboardless DIY DAS system using a cheap 2U rackmount case that takes a standard ATX power supply and can fit 16 2.5" SSD's in it. The SSD's will be used in a mergerfs pool backed by snapraid and vary in size from 512GB to 2TB. Because it's going to be using a union filesystem then the througput doesn't need to be that high, as only 1 disk at a time will ever have IOPS most the time, the only exception being when syncing snapraid. Because of this, I'm connecting all 16 SSD's to two of these SAS passthroughs and connect them to the quad port HBA on my server. 6gpbs will be plenty because this will be JBOD non-raid.

My main question would be if anyone sees any obvious problems with this setup. As far as I can see, this should work to cheaply expand the storage on my server.

There are also a couple of things I'm hazy about regarding power: I'll be using a standard ATX power supply and obviously will be powering the SSD's, but is that all that's needed? I'm assuming the SAS passthroughs don't need power?

Also, is there a way to get it so that I can connect my main server to this DAS using only one cable? It would be more convenient than having to run the 4 SFF-8088 cables from the passthroughs to the quad-port HBA on the server. Obviously it would require swapping out the quad-port HBA with something else, but I'm not sure what and was wondering if anyone could point me in that direction.