Base in Florence or move hotels?

It all works. There is not a "perfect" solution. You can day trip from Florence easily using public transit. I would not rent a car unless you are in areas not service by public transit. And a car in Florence is a real pain in the butt. And many of the towns have very limit and sometimes difficult to find parking areas.

Even if you don't visit a lot of museums, the architecture of Florence make the city a fabulous museum, and just walking around the city, you could easily spend all five nights there without running out of things to see and do, especially if you take a day or two for day trips to nearby mountain towns.

If you decide to break it up, 2 nights in Siena and 3 nights in Florence would make sense. I would suggest doing Siena first, because Siena is medieval and Florence is Renaissance, and it makes more logical sense to see them in that order.

Since you are flying in and out of Rome, I would NOT spend two days there, travel and then spend another night in Rome.

It is usually recommended, and makes perfect sense, to drive/train/bus to the area that is farthest away and then come back and spend the last few evenings in the city which you leave. I would train to Florence as soon as you arrive and
stay in Florence for a few days, there is so much to see and do, and you have the option of hopping on a train (Lucca, Pisa, etc), a bus (Fiesole, Siena) or just walking around the magnificent city. You could always take a tour bus to a winery in the area, visit the American Cemetery just outside Florence (think Arlington in a beautiful valley), etc. The architecture there is amazing and you could spend a good part of an afternoon climbing Bruneschelli's dome or walking up to Piazza Michangelo and watching a sunset you'll never forget. Then, train back to Rome, stay 3 or 4 evenings and fly out of FCO. Good luck!

Marie

^^^^ What Marie recommends makes perfect sense.

I like your original plan. I can't imagine training out of Rome immediately upon arrival. It's Rome. If it feels right to you to get settled in Rome for a few days before moving on, you should do that.

And your plan to base in Florence makes sense because its train station and nearby bus station make it so easy and simple to day trip out. Basing in Florence makes it easy to keep your options open for your Tuscany plan, and your return to Rome.

If the focus of your trip is Tuscany, make sure that you spend most of your time in Tuscany. In Val d'Orcia (an area of Tuscany) for example you will have walking/hiking, bicycling, marvelous food, splendid vistas, a lot of history and architecture in those hilltops villages. I love the train, but for Tuscany rent a car and study the map to find the most scenic backroads.

In contrast Florence will be very crowded in July. I would not based myself there unless the focus of my trip was the Renaissance.

Why don't you (like it has been suggested above) train directly from Rome into Florence on your first day in Italy. The next day rent a car in Florence and go and discover the beauty of Tuscany.