I've read a LOT and zeroed in on a NanoPi M4 (but discovered V2 before paying). So I have a bunch of parts; a couple of racks; a couple of 2Tb drives; some cables; old computers from which I should be able to pillage a PS; and I'm waiting for some copper shims for the heatsink—should be here in a couple of days. Maybe in another week I'll have something up and running.
Thanks for the help getting me to this point!