Yes, that will be enough. You can also use a single port on the NIC and the one on the motherboard if it can handle the ethernet speed you want.

This is my network setup on Proxmox: Image

vmbr0 is a bridge that has a single port going to the modem. The OPNSense VM’s first virtual interface is connected to this and configured as a WAN interface. Nothing else connects to this bridge as it is exposed to the internet.

vmbr1 also has a single port that goes to the physical switch. OPNSense’s second interface connects to it as a LAN port, as well as every other VM and container running on the server.