How many PCs will I need to build this homelab?

[meyergru]

The memory footprint of OpnSense is independent of the number of VPNs (at least with less than 20 of them).

You can run any VM on Proxmox, but if it is not running for whatever reason, the VMs do not run either. Adguard Home does your DNS, so without it, you do not have internet access, therefore I would run it on the OpnSense hardware. So, run anything that is vital to your network on OpnSense, the rest on Proxmox.