A:AnswerThis does have an ethernet port. But if you are looking for ethernet without adding other ports, you can get a USB-C to ethernet adapter cheaper.
A:AnswerI'm no Pro but I recently purchased this not too long ago and use it quite a lot since I started my own podcast but to be clear, YES it does use up power while connected whether the laptop is open or closed.
I always disconnect it when its not being used but I would suggest turning off your device completely when not in use if you truly wish to keep it connected at all times