Congratulations, and welcome!
What you should do is make a list of all the things that will plug in and do the power draw in watts. If there's no watt rating on the device but it shows amps, then amps times volts equals the watts.
Figure in a battery charger - you will probably some day want to be able to run the lighter loads from a battery bank through an inverter instead of 24/7 generator. State campgrounds up here allow 5 specified hours per day of genset use. I suspect even liberal ones have quiet hours at night. It all depends on where you intend to park, plus allowing flexibility for changes in plans.
When you get the total, add at least 1/3 both to allow for things you haven't thought of yet, and to relieve the strain on the genny. Buy the next size or two up. If you figure this, your question will eventually answer itself.
A too-big genny will waste fuel (I know one pair of too-big gennys that each burn either 30 or 60 gallons per hour AT IDLE!).
Too small a genny will be stressed and have a shorter life.
Good luck, and nice looking bus.