I like this build, the author basically puts an electric box in the wall and has all the electronics in there. Good idea. But… Not to thrilled with the wiring job. I am pretty sure thats not up to code. A better solution would be to put a side mount outlet and then plug in direct. Less likely to hit issues there.
https://www.instructables.com/id/Flush-Wall-Mounted-Raspberry-Pi-Touchscreen/