Alternate itinerary?

We recently spent time in Verona, Padova and Bologna and enjoyed them all very much.
You do already have 8 nights in Tuscany so if you don’t want to repeat Florence, maybe consider one of those locations? All easy to reach on train.

3 nights Bologna with day trip to Ravenna
Or
3 nights Verona- could day trip to Garda/Sirmione

Assuming you are getting a car for Siena/Montepulciano? Where will you pick that up if not Florence?

I enjoy attending festivals. This one is in May in Ferrara:

Il Palio di Ferrara: Ferrara hosts a historical horse race dating from 1279. It is run the last Sunday in May. There are parades, flag throwing contests, and other events every weekend in May including a historical procession to the castle with over 1,000 people in Renaissance costumes on the Saturday night of the weekend before the race.

We had a wonderful meal at Trattoria da Noemi. From Ferrara, it’s an easy train over to Ravenna to enjoy a day seeing the gorgeous mosaics. Also check out the mosaic museum. I’ve stayed two nights at Ravenna - a nice town, but you could do it as a day-trip.

You can take a direct train from the Florence SM Novella station to Lucca (1h 20m) but direct trains are sporadic so you may need to get an early start.
Will you be renting a car? If so, Siena would be a good place to pick it up to explore Tuscany.

Not sure why you are spending four nights in Siena.
We visited that town and spent two nights and pretty much did the town.
I would advise reducing Siena to two nights and Montepuiciano to 2-3 and add days to Rome. Three days in Rome are WAY not enough.

OP is spending 4 nights “30 minutes from Siena”
I assume at an agriturismo

I would consider cutting nights somewhere else and adding Orvieto.

Christine, I like your suggestion of Verona x 3 days and a day trip to Garuda Sirmione!
Jean, the festival sounds great but our trip ends before then.
MaryPat, yes, we will be renting a car but not sure yet. Lucca is still a question mark, but Verona sounds better to me.
I know many of you use Autoeurope, what about Europecar? It seems like Siena is not a pickup city with Autoeurope. Florence is an option although out of the way. Any other suggestions?
Christine is correct. We are going into Siena one day and will explore the area around on the others. I am still thinking about dropping one night from Montepulciano and staying overnight In Orvieto. We have both been to Rome, so 3 nights is okay.
Your help is wonderful.

Not sure where you are looking but Siena is a pick up place thru AutoEurope
https://www.autoeurope.com/

AutoEurope is a consolidator offering cars thru Europcar, hertz etc
Europcar is the car rental company
There is a Europcar location in Siena, also Hertz

If you end up in Verona you’ll need to train to Tuscany somehow so Florence train station car pick up probably makes most sense
The rental agencies are all right there close to SM Novella

There are tons of posts here about picking up in Florence

Kathy, AutoEurope was the vendor I rented my car from in Siena.
Another idea is to rent a car in Florence and get on the Chiantigiana Road (SR 222) to Siena and visit Chianti towns along the way (1h 45m). I know Florence ZTL laws are strict so make sure you learn more to avoid hefty fines that arrive in your mail box six months later. The price of a ticket accumulates as time goes by.

I liked Bologna and it's very convenient for day trips by train to lots of other enticing places - Ferrara, Modena, Parma off the top of my head. I rented from Europcar a few months ago, pick-up and return at Florence airport. It saved me all the worries of the ZTL's in Florence and it's easy to get to/from the train station to the airport by tram.