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.
As a professional musician and someone who works for a prominent Japanese electronic musical instrument company, I’m going to have to disagree.
Thunderbolt provides all the low latency of a PCIe interface with none of the drawbacks. I use an Antelope Zen Tour in my home studio and it is just amazing.
The systems I designed for work though use RME PCIe cards, but those systems aren’t in the hobbyist space.