Well I think sit sort of near the top of the scale, a bit of 4 and a bit of 6 but I am no mechanic.
I have rebuilt a cylinder head(on a mini)
I have changed loads of head gaskets.
I have done welding fabrication to make stuff like seat brackets, 5 link rear end, engine/gearbox mounts.
I have put an engine in a car it didnt belong in.
I had a go at an efi wiring loom but I didnt have an accurate diagram and had to get a pro to step in and finish it off.
I havnt ever needed to rebuild an engine.
I have done small amounts of spraying(just one guard).
I have done loads of welding rust repairs(MIG)
I have done stereo installs(I dont do stereo anymore cause they add weight).
I've made a cold airbox, welded up steel intercooler piping.
All machining I have to outsource cause I dont have/afford to buy a lathe or milling machine to do stuff like shorten propshafts and drive shafts and cutting splines and what not etc....