Copper slip on threads is bonkers. Good post!
Good point re cold engine too. Well worth remembering, although in winter it's tempting to change the plugs when the engine is warm so your hands don't freeze!
Fair point about how tight is hand tight? For me it has been down to servicing my own motors for 30yrs and experience. Touch wood never had a problem, but first turn of the key post plug renewal always comes with a little mild apprehension! Torque wrench is safest for sure though.
Wheel nuts. F. tight is how tight.
Hard to over tighten yourself I would imagine. For sure, wheel places with their air guns can be over zealous, but I doubt anyone would over tighten their own nuts.
What is worth remembering, is to check they are tight again after several miles.