3) Coil the wires in a circle if they are too long

wouldn't it be better to coil them in a figure eight then fold it in the middle to make a single coil? I use this method when ever I'm wrapping any cable. there is a way (which is too complicated to explain here) to coil it in figure eight fashion in one coil in one hand. This way the current is flowing in opposite directions with each turn, cancelling itself out. It has the added benefit that there are no twists in the cable and it sits flat.
However, if possible, and as it's an installation, the cables should be trimmed to the correct length. More cable, more chance of induction.

4) Thread them through a ferrite torus

I'll have to try this one too!

Murray 06000047
I don't think, therefore I am not.