When going to the drive through at a bank, what is best for my engine etc.... for the 5 minutes doing the paperwork, should I stop the engine and restart it later, seeming to tear it appart, or should I just leave it on, even if it gets a bit too warm, idling hard and stuff and gas goes by?

 

Leave it on, but put it in neutral. Idling isn't great for an engine, but neither are startups (hot or cold). Exception would be in certain smog-laden cities. Detroit isn't too bad, but we have "Ozone Action" days where the exhaust affects the ozone more on higher temp days.