You'll have the loom under the seat for the pre tensioner, airbag (yellow cables) and obviously for the motor.

When I did mine I chopped off the plug from my original seats , leaving some wiring, chopped the plugs off the ST seats and then reattached the old plugs to the st seats using connectors for the relevant wires (they should be the same colours).

I also cut holes in the rear door cars for the winders and used the existing door pull surround (so it didn't look out of place and didn't mean I had switches doing nothing)

I haven't yet wired my seat height adjustment in but I'm going to run a wire under the centre console (fused btw) past the glove box, under the wing and onto the battery. Earth I'll pull from where the seat mounts to the floor.