Go with something with zfs
I built a server with a bunch of second hand parts, a case + dell xps mobo I bought off marketplace, a pair of 6 tb, pair of 3 tb ( I had one and bought a matching) plus a 500 gb SSD for the os, 2x16 gb memory sticks.
I'm running fedora 36 with the openzfs dkms module ... Gives me what I needed to replace a couple aging arm based nfs units (a Lenovo and a buffalo Link station). I'm running 2 pools with each pair of disks in raid 1. Maybe not the best config but works for me
Ubuntu also ships with zfs but I think I read something about it possibly being removed in the next version
You could also use btrfs as it would allow you to add mixed disks into a volume and share that out via nfs, samba, open media vault, etc but I'm really not sure about much more than that. I think Jás did a presentation about butter face a couple years ago