Oh, I've used more than that. And less. And none at all. It all depends on the paint, the contours of the model itself, the effect I'm trying to achieve, the phase of the moon, my mood at the time, etc etc etc.
For example, here's a couple I used no clearcoat on, just rubbed out direct. I was going for a Day Two (factory finish) look on this MPC '69 Camaro, so I laid the Model Master Brit Green on as smoothly as I could (airbrush) and then gave it only a very LIGHT rubout, normally a no-no with metallic paint, but I thought I could get away with it. And I did. I deliberately left just a hint of "orange peel" for a factory look.
This AMT '62 Vette got three or four coats of Model Master Honduras Maroon from the can, also rubbed out direct (no clear coat) as an experiment that I think worked.
Dan, I'd love to hear your opinion of these.