If it's attached to the wall theres probably bare metal on the bottom, and if not there's definitely some on the inside when you open the door. Just any bare metal on it.

Absolutely, if full local control is what you want and you expect to get more devices then it's worth either reusing an old computer for home assistant or getting a home assistant yellow.

I'm running an Ender 3. Although through the 3.5 years I've had it it's had so many parts changed and upgraded it's turning into a real ship of Theseus. Upgraded the mobo, hotend, direct drive extruder, raspberry pi for octoprint, enclosure, and bltouch for bed leveling.

It's definitely been a rewarding hobby, learning to use fusion and building things from scratch.