I don’t know why the timing belt would see any difference between normal and towing service. The engine operating temperature as controlled by the thermostat would be the same. Who could say that the extreme vs normal service result in more or fewer engine revolutions and therefore more or less belt flexing? I’d go with the normal service for the belt. If only one belt mileage/time specification is provided, then that is what you must do. No timing belt in any brand that uses one can go indefinitely.
Yes, change the water pump if it is driven by the timing belt and change the tensioner or tensioners too. A failed pump or tensioner can take out the belt so new is installed as a precaution.