[AZLiberty]

Once - maybe.

Like fitting a suit, it should only need to be done once.

Unless your playing style radically changes there should be no need for a setup. The point of a setup is to fit your playing style, so a factory setup might be too high or too low, but once adjusted it's not going to change. (assuming you don't let it dry out from low humidity - but that doesn't get fixed with a setup that gets fixed by humidifying the instrument)