help with itinerary

Arrive Florence via air (if you can't find a flight and must fly through Rome, take a fast train from Rome to Florence). Visit Florence for a couple of days.
Visit Tuscany. If you rent a car do so after visiting Florence. Stay outside of Florence once you have a car. Stay in Tuscany (countryside or small town) base for at least 2 nights, better if more. Once done with Tuscany, drive to Orvieto from Tuscany base. Keep the car if you plan to visit Civita di Bagnoregio. Return car in Orvieto, visit Orvieto. Train from Orvieto to Naples (possible train change in Rome). Then from Naples take circumvesuviana train (or a boat) to Sorrento. You can stay in Sorrento or Amalfi coast, e.g. Positano (bus from Sorrento). Stay there at least 3 nights. 4 even better. Visit Amalfi coast, Sorrento, Pompeii, Capri island, Procida island, maybe Naples (museu Archeologico). No car needed in this area. Fly back to the US from Naples (via European hub), if you can find a good flight (you should spend the night before flight in Naples). Otherwise, if Rome flight is more feasible, take train back up to Rome. Spend the night before the flight in Rome. Or more nights if you intend to see Rome again. fly out of Rome.

Roberto is 100% correct about the best way to do your trip.

Thank you!! After looking at all the places we want to visit, we think we will keep the Amalfi Coast for another visit. This time we will fly into Florence as suggested. Stay a few days there. Then split the time between Sienna and Orvieto. Should we then fly out of Rome from Orvieto? Suggestions on favorite hill towns?