Itinerary Review?

Looks good to me. My question is you mention you aren't city or museum people, then why stop in Florence? I would maybe take out Florence and add in 2 nights lake como. You can fly into Milan and quick hour train ride to Varenna. Then Varenna to Milan for a train to Venice and continue thenitenary above. Just a thought.

Siena to Rome you could take a train and stop in Orvieto. It's on the train line. Or do that as a day trip from Rome.

You pretty much have all the Tuscan towns covered. You can probably squeeze in Pienza between Montalcino and Montepulciano since its in the middle of those

Is your cooking class booked or know where you want to take it? I did one in Volterra couple weeks ago at Del Duc from Ricks book. I loved it. Claudia and her mom were amazing. I'm going to make the meal I had for folks in Tampa and another other message board forum people who want to drop by.

I think it would be more efficient this way:

Venice --> Florence -->Tuscany/rental car --> Cinque Terre (maybe drop car in LaSpezia) --> Rome

Otherwise you are backtracking to/from the CT (which is probably your longest travel time).

I would add Torcello to your Venice stay, maybe even replace Murano with it. Torcello is the original settlement snd still has the historic feel you may be looking for. Beautiful mosaics in the church there, small enough so it's not like a museum visit. Burano has great artisan studios for glass.

Perfect. Great first trip. Visiting the big 3 in the right order, plus great side trips to CT and Tuscan countryside.
Answering your questions--
1--yes
2--yes, minimum for Venice and Florence but it lets you add CT to the trip. Personally I would add a day to Florence and subtract from Rome but that is strictly personal.
3--we like to bounce from big city to small town and back so I like the rhythm of your trip.
4--we always drive. (We're car, not train, people most the time). If you flip days for Volterra and Montalcino you could go to Montalcino on last Tuscany day and stay That night there and leave from there. No doubling back. But packing and unpacking another night. Maybe briefly stop in Orvieto for lunch on the way to Rome.
5--for a first trip, you have chosen two great day trips to see major hill towns. Lots of others you could pick, but these are good ones to start with. Easy to drive to and park. Each worth a visit on your first trip.
6--bring twice the money and half the clothes?
Enjoy

Thank you so much for all of your comments! We haven't booked anything yet, so I'll be thinking of each of your recommendations as we solidify our plans. I think for this trip we will keep Florence. We aren't huge museum people, but part of me can't imagine going to Italy and not seeing at least some of the Rennisance masterpieces that are there. We will just break it up with walking around with Gelato :)

Skip, we are also typically car people. I think that is part of the reason this trip is throwing me for a loop! If we drive down to Rome, where is the best place to return the car to avoid all the ZTL?

To add onto Skip's comment, if you choose to stay in Montalcino look at Palazzina Cesira from Rick's book. I stayed there a couple weeks ago, the owners were real helpful with the wineries around the area. Roberto also makes fresh eggs for breakfast which are amazing. After being in Italy for 2.5 weeks and eating the italian breakfast if was good to have some eggs for a couple days. He'll make them any style you want.

Others may have more options about the Rental Car return. If you stop at Orvieto on the way to Rome you can always drop the car off there and then train into Rome. Or if you drive further into Rome and if you use Europecar you can return it at Tiburtina station. From there you are only 4 stops on the metro from Termini. You'd have to check if other car companies have a rental there other then Europecar though.