I have two electrical circuits in the darkroom - one for the enlarger and timer with a voltage stabilizer, and one for everything else. It is very important to have a ground-fault circuit interrupter in your darkroom to prevent serious electrical shocks especially when working close to water. The switch for my general circuit is located outside the darkroom and powers everything on or off. I included a red light on the outside of the darkroom to let you know if the circuit is on or off and if the door is closed and the light is on family knows not to enter.
Plumbing is copper and is mounted on the wall surface so it can be modified as required without having to open walls to get at it.
Darkroom is 10'x14'
Regards
Gord