I don't see why you'd want separate clusters, just stick em all in one.

Yeah but Vince is a dinosaur. I've heard he's still running OpenVPN. Eeeww.

16gb is fine, but you'd probably want to stick with containers. I had an S12 Pro with 32gb working just fine.

2 vdevs with 10 x 10TB drives in RAID-Z2 would give you around 150TB useable.

So you could do that with one vdev and 10 x 20TB disks, but you wouldn't have as good performance and 20TB disks take a long time to resilver if you have to replace one.

I run a wireshark server, with the client installed on family members laptops/desktops to auto connect.

I then just connect from my desktop to wireshark and can connect to their devices.

I'd probably do 4 x 10 disk RAID Z2 vdevs. Probably just under 600TB useable with 20TB disks.

This all sounds like pipedream stuff though, to have that much storage requirements but not really have any idea of RAID, parity etc. and you're somehow also backing this up somewhere too.

No QuickSync on Xeons. Use the Optiplex.

Maybe find a cheap E5-1680 v3, and replace the 4gb sticks with 8gb.

Debian.

That's ancient, so no it's not going to be able to handle that.

The Zimaboard is way overpriced, for a way underpowered CPU. Unless you specifically have a need to use its PCIe slot for something, I see no reason for it.

As others have noted, an ultra small form factor PC, the likes of Dell/HP/Lenovo sell is always a better value option.

I use Technitium DNS for all my DHCP/DNS/Ad Blocking.

https://technitium.com/dns/