I intent to use another NIC through a usb port. I want to be able to physically plug/unplug it. Is this possible? References on how to do this for a beginner are much appreciated.
It's possible, but not something I'd like to try without a really good reflow oven, 20 Pis I planned on throwing out anyway, and the assistance of someone with steadier hands. The parts involved are tiny surface mount things. You'd have to hot air or, more likely, oven the board in order to tweeze them off and clean up any soldery mess, and I can't find any references that would indicate the behaviour of the Pi afterwards. I would strongly discourage a beginner from making the attempt.
If you're looking to turn off the onboard Bluetooth and WiFi, there are some suggestions against jww's question here, including blacklisting the drivers and adding options to