I don’t know anything about Unbound and Opnsense, but it seems like your DHCP settings should set something as a nameserver for the clients.

If you’re forwarding from the “router”, it would just be the router’s IP. If you look at your clients, are they getting a value for “DNS server” from DHCP?

I would expect it to be 192.168.0.1.

You could try. I doubt that you’d get more than a few hundred bucks for that setup in the US. Racks are almost free, and a v3 64GB sever is maybe $300-$350, shipped.