Ciao again!
For driving time from Chianti to Cinque Terre (Rio Maggiore is the first town you reach so you could start from there), you should calculate about 3 hours. It is definitely easy to reach by car, but once you're in the first town, you should use the train to move between the five towns as it is easier to use.
I am glad you are including it in your itinerary - we definitely also plan to go back next year to help the towns get back the tourism they desparetely need to rebuild Vernazza and Monterosso after the major flood they had at the end of October.
As to your itinerary in general, I think it looks perfectly fine until the day after Siena.
If you want to see Pisa, Lucca and the Cinque Terre (which are five separate towns), I definitely think you should give yourself at least 2 days to do that. Maybe do Pisa and Lucca on the first day, arrive at the first of the five towns in Cinque Terre, sleep there and then spend the entire following day visiting them - they definitely merit the time!
You have a day to drive through Val d'Orcia with the following day Montalcino, Montepulciano and Pienza -- but these three towns are all actually in Val d'Orcia so this actually frees up a day to spend between Cinque Terre and Pisa and Lucca!
If you're staying somewhere central the whole time in Tuscany, somewhere like Palazzo Malaspina or elsewhere in Chianti, I'd suggest some slight changes to the plans after you leave Venice.
2 days in Venice
1 day driving from Venice to Cinque Terre, with a stop in Modena to visit Ferrari museum (the museum is actually in Maranello, about 19km outside of Modena)
1 day in Cinque Terre (sleep there)
1 day visiting Pisa and Lucca, head on to your base for the rest of the time in Tuscany
2 days in Florence
1 day in Siena
1 day driving through Chianti and San Gimignano area
1 day through Val d'Orcia - including Montalcino, Pienza, Montepulciano
3 days in Rome
How does that seem to you? This way you take the drive from Venice and move south and west first without having to do backtracking and spend time driving all over the region. Once you're in your base for the week, will have day trips each day in different directions, always returning to your central point.
