Tuscan Hills and Rental Car Intricacies

I think your plan sounds fine. Be careful about where you drive in Florence. It's easy to accidently drive into a ZTL. As for hill towns, we thought 2 per day was enough. Siena is big enough for an entire day.

We did our 3 night stay in Florence first then rented a car for 6 days and dropped it in Spoleto and took train to Rome from there. Your plan is certainly doable but I would not care for the "backtrack" or the need to be driving in and out of Florence more than once.
Many suggest dropping a rental car in Orvieto --we skipped Orvieto and were heading to Rome from Assisi so Spoleto made more sense as a drop off.
Many do Siena as a day trip then rent car as they are leaving Siena- thus avoiding driving in either Florence or Siena.

I would first plot out exactly where you will visit in Tuscany- then see if a different drop off location would work better.

That said-I do highly recommend the Hertz Via Sansovino location in Florence- it is well outside the ZTL- we took a cab from our hotel near Duomo (about 8 euros) and had a super easy time leaving the Florence area from there.
I'm also not sure I could arrive in Florence then leave town right away without FIRST seeing the Duomo or any sights in Florence actually. ;)

I would try to avoid a round trip rental car in and out of Florence. On our recent trip to Florence and the hill towns, we started our trip in Florence (4 days), then took the bus (easy and cheap) to Siena. We rented our car there and stayed nearby in an agriturismo, which made for easy day trips to surrounding hills towns and simpler drop off. I would highly recommend a day in Siena by the way. Orvieto could be an alternative to Siena for car rental too. I also agree that round trips tend to waste time and sight seeing options and don't cost much more.

As for base towns, I would highly recommend an agriturismo. We stayed west of Siena and did day trips north to Volterra and San Gimingnano and south to Montalcino, Montepulciano and Pienza (2 different days). Long days but doable. Alternatively, you might want to consider 2 locations to minimize driving time. Montepulciano would be a great option....our favorite hill town! Have a wonderful trip!

Montepulciano would be a great option....our favorite hill town! Have a wonderful trip!<<

Our favorite as well. We stayed in Siena 2 nights, then Montepulciano 2 nights.
bnelson210- if you would like a recommendation for a fabulous place in Montepulciano with convenient parking -PM me

That would NOT be my plan.
Mine would be:
Train Venice to Florence
Stay in Florence for 3 nights first (no car)
Rent a car in Florence after the 3rd night, head out to Tuscany/Umbria to visit villages and countryside by car.
KEEP CAR AND DRIVE TO SORRENTO.
Once in Sorrento return the car (or keep it if you want).
Finally go to Rome (by train, or car if you kept it)
The best base is somewhere along the Florence Siena freeway. The Alta Vald'Elsa (Upper Elsa valley), like Colle Val D'Elsa or Monteriggioni (or around there) is nice and central to everything famous

If someone has a great recommendation for a place to stay in Montepulciano , I would like to hear about it.

I concur with other posts. After train to Florence, stay there, then upon departure, pick up your rental car. Don't back track to Florence, but maybe drop car in Orvieto after spending a night, then take train to Sorrento (you'll need to change trains in Naples).