USB 3 should drive enough throughput to do that if you want.

The NanoPi R1 looks interesting but lacks the software support on mainline / upstream that RPi has https://www.friendlyarm.com/index.php?route=product/product&...

You could buy a ( usb -> ethernet ) cable for less than 5 dollars.

I use ( usb -> ethernet ) for the rPi zero.

You even get ( usb -> ( ethernet, usb, usb , usb ) ) accessory, which is really cool.

I have one of the larger ones (3 usb + Ethernet). I received it as a gift and was originally skeptical of the usefulness of the usb ports vs the size tradeoff, but it turns out to be super useful. It stays on my desk with my mouse, keyboard, and printer plugged in, and acts as a pseudo-dock for my laptop. Very nice!

Use VLANs to separate the external/internal connections.

That requires you have a switch on the other side that supports VALNs -- something generally a lot more expensive than the Pi itself.

Pretty sure there is one orange pi or Banana pi for that.

Probably better going for something like the Espressobin or even a C3000 series Atom.