Don't even consider Naples, beside being a dump, you can't park there. Florence is awesome and if ramp parking is available, its 150Euro a night, if there is no ramp parking you can get hangar parking for 500Euro a night. An awesome city in Italy is Perugia. It's about 1 hour drive south of Florence..they got parking, and beautiful little town..Hotel Brufani Palace, the place to stay. 2 days is all you need to see Perugia...
rent a car and cover the whole Umbria and Tuscany sections of Italy..you won't be disappointed. The food in Northern Italy is the best in the world.