

Lines F and E don’t exists in your diagram, all your VMs inside of Proxmox are accessible and sharing port eth3. Except Opensense, as its not bridged to eth3, but instead is assigned to the NIC card you have.
OPNSense inside Proxmox is the only VM that will see the NIC card and be the only VM that uses that NIC with those interfaces.
One interface would be for WAN in like you drew, and the other is the LAN port like on any other router. This LAN port needs to connect to a switch as this is where your OPENsence will communication with the rest of the home network and handout DHCP addresses. It’s also how you would reach your OPENsense GUI through a browser. (Outside of managing it within Proxmoxs GUI, accessible on eth3)
If your OpenSense VM goes down your home network won’t have a router which means no PCs would be able to communicate as they would have no DHCP addresses, so even if all your communication is “inside of Proxmox” your VM still would not get a DHCP addresses.





















I wonder if theres a possibility to line a spaceship haul with this stuff to protect from cosmic radiation.