I did mine recently - tips I can think of are;
Make sure you have some spare bulb holders
For both rearl ights I used the twin bulb holders, the left one I only wired up the 5w side of a stop and tail bulb as this was 'lights on'. On the right side with the fog light I wired both filaments in and have the 5w as the normal light and the 21w as the fog light for Mr MOT man.
I tried to get the reflector out for the fog light to make both match but its a right pain tbh and looks ok to me with it in and the lights on.