Back in the day I ran a pfsense VM on ESXi before broadcom bought them. I found it easier to just purchase a cheap Unifi AP and spin up a VM for the Unifi controller app (I’m assuming you can still run that on your own hardware, its been a few years). I think I got a UAP 6 lite or something like that. If I recall it was about $130 CAD with the PoE injector.

Techincally its not ideal to run your firewall on the same device as other things, but I never had any issues.

Also, does the mini PC have multiple NICs? You will have a bad time if it does not.

The snap version of nextcloud has been pretty solid for me, except for the time that I installed the nextcloud backup app.