Fantastic idea to protect the walls from the inevitable in a garage. One thing you might want to pay attention to, is you put the pressure treated wood directly on the concrete. Usually you put a barrier between. It will probably be fine for a very long time, but just check it now and again.
Good question. I’m not an electrician but when you cut the hole in the steel panel you could keep and tab and bend it into the electrical box. That would allow you to screw the ground wire to it.
The screws are long enough to go into the studs. I mark the stud locations on the bottom board before putting on the steel so I know where to put the screws.
