probably a very common question
but Im buying a high end mini pc with lots of RAM and lan ports and hope to utilize its full power in many vms (I have another old desktop with truenas that same apps)
what are the best practice
option one (cancel the high end mini PC and get a low end one just for opensense?)
option two (buy it and use it for proxmox and virtualized opensene )
Both options are just as good. Your choice. No "best practice" for this. As long as the hardware is compatible with freebsd (avoid Realtek NICs), then is just what you have available for your chosen budget and other preferences.
I never like virtualizing my firewall due to the prospect of vlan hopping attacks. But this really comes down to what you need. If you need to have Proxmox running, and you can only afford 1 machine to do everything, then you kind of have your decision.