Italy itinerary

Seems to me that you're doing a lot of jumping around to try to see it all, but this itinerary is going to require a lot of travel time between destinations (Italy is bigger than you think!). I would cut it down to 3 or 4 overnights in order to maximize your time in cities, rather than constantly being on the move.

You mention that you've already been to Italy a few times, so I'm not sure whether you've been to Florence before, but only 1 day there doesn't seem at all enough time. Instead of Florence, have you considered staying in Orvieto? It's right in between Rome and Montepulciano, so might be more convenient to overnight there, instead of going all the way north to Florence and backtracking to Montepulciano.

Yes, I have been to Florence before. My husband has not though but he's not interested in going inside museums and such. More so just for food and seeing the city from the outside as we walk and stroll around. So we feel that one day will suffice for that.

I did not consider Orvieto - but would that mean more windy roads to travel to other places?

Since you have two days pending and Florence has very strict ZTL zone laws pertaining to car rental, why not take a direct bus from Florence to Siena (1h 15m) and sleep there a couple nights? Siena is also a good place to rent a car because there’s less room for error when it comes to ZTL laws.
The most scenic drive from Siena to Pienza and Montepulciano is along the Sienese Crest Road. Siena is also a wonderful place to be at night with excellent restaurants.

Word of warning regarding "late train to Varenna". Milano Centrale can be a bit hectic and trains are on occassion cancelled. I'd suggest trying to catch the next-to-last or one before that from Milan to Varenna. Miss the last train and you are stuck. I speak from past experience! Due to issues at another station we were delayed and nearly missed the last Varenna-Esino train for the day.

I have been to CT. Glad I went but there is no allure to return. We base at least ten days every trip out of Varenna. Best of luck!

I highly recommend Orvieto too! We took the train from Rome & rented a car in Orvieto. We stayed at Agriturismo Antica Olivia, which is a working Olive farm! Loved it. You can take a day trip to Civitia di Bagnoregio. It's awesome & worth the climb up the hill to see the village and the views. From there we drove to Tuscany and stayed outside of Siena at Agriturismo Marciano, which was wonderful. There are so many small towns in Tuscany to explore by car.

Another vote for Orvieto! You’ll only be an hour’s drive away while in Montepulciano and it fits in nicely on day 7. While Orvieto’s cathedral and town are impressive, the pre-Roman Etruscans had an underground city here which you can tour. You can return the car in Florence and take the bullet train to Milan en route to Lake Como.

You didn't mention how old your daughter is but as a fellow motion sick person I sympathize! Oriveto could be a good stop - you could even train from Rome to there and then train again on to Florence. Orvieto has a really cool well you can walk down into which I thought was super cool. There also underground tunnels and cisterns that you can tour but I have not been on those. Lucca could be great, also on a train line from Florence (trains seem to go in straighter lines than some of those roads and I often feel better after the train that a car ride). Lucca has great city wall with a very wide promenade the whole way around the 3 mile loop. We have been there several times and have both walked and biked around (easy bike rentals). The path is all flat and sits up above the town itself so you really get to see the town. You could feel like you go some Tuscany and she won't be miserable arriving by either car or train. Renting a car in Lucca would also be much easier than trying to get out of Florence, unless you pick up the car at the airport which I 100% recommend there. How about Montalcino instead of Montepulciano and Pienza, based on my experience with the windy roads, unless you are taking the "longer way" on the A1 from Florence and skip driving on the smaller more local roads closer to Sienna. Montalcino has a cool castle you can tour and has stunning views that feel like they go forever. Could be worth an overnight but you need a car. Have fun!

Orvieto is definitely on my radar for a future trip and I was even considering it as a day trip from Rome but was not sure if April is a good time for olive oil tasting