It can be just like you’ve said. You can also run tailscale directly on the system hosting a service and access it directly over the tailscale network.

Just use Snapraid & MergerFS. No special Hardware required and you don’t need to change what is on your disks.

From a quick search: https://perfectmediaserver.com/02-tech-stack/snapraid/

This honestly sounds like the best solution to this particular problem.