Be sure to check OPNsense Ethernet card compatibility. When I built my router, it was strongly advised to stick with genuine Intel PCIe network cards. And I’d personally strongly recommend against using a USB to Ethernet adapter. To many reliability issues with the USB side of things.
In a non-conventional setup test, I tried an old Mac mini with two thunderbolt to Ethernet adapters and while OPNsense worked, stability wasn’t optimal.
Of course, your mileage may vary and genuine Intel PCIe cards are quite a bit more expensive than a USB Ethernet adapter.