Could you buy a used corporate SFF off of ebay instead of building a new rig? Maybe an optiplex, Dell 12-core, Thinkcenter, or some sort of multi-core mini micro? You could even buy 4-cores but cluster 3 of them together to make 12. That’s Docker’s best use case, mobilizing your VMs across a cluster of machines. I’m not sure what you need but this is a lot of power and cost. You could start really really small with an Unraid and Plex server to dip your toes in, and then you’d have an idea about hardware and expanding your power incrimentally.