I would always recommend one thermostat per heating zone, otherwise what’s the point in having separate heating zones? (You can balance your heating system without the need for separately controlled zones. Okay having a separate heating zone does mean you could isolate and turn one of the zones off if the space is not in use, but you still need a controller to do that, so why not make it a thermostat. ) My new home will have 9 heating zones, with 9 thermostats so they can be individually controlled. The home is on 4 levels and some of the house is not used all the time.