It’s a midtower case so I just went with an ATX board. I would like to figure out a compact solution for the future but it’s hard to house and control a bunch of HDDs in a small footprint. I don’t want to spend thousands on a NAS and I haven’t found a trustworthy DAS solution that will hold all my drives.
You might play around with PCPartPicker since it allows for so many filtering options for things like SATA ports on a mobo or drive slots in a case and see what you can come up with.
Check /r/opensignups on reddit and make sure you read the rules of the trackers you try to join.