Florence, Siena, Cinque Terre, Sorrento

Sorrento is the real outlier in your agenda. You're probably going to spend at least 6+ hours getting from CT to Sorrento and 5 or so getting back from Sorrento to Florence. Train from La Spezia to Florence, fast train from Florence to Naples and then probably the creaky circumvesuviana train to Sorrento. I would suggest replacing the only really southern destination with something more northern and not spending so much of your limited time in transit.

Your 3 nights in Siena is only 2 full days there. You could easily spend that time in Siena itself, but if you wanted to explore the area you either rent a car for one day or do an organized tour. I usually suggest tours to people but with four people if you decide on a single agenda and some one is comfortable driving in Italy a San Gimignano and Volterra loop or similar could be interesting.
Make sure whoever is going to drive get an International Drivers Permit before leaving the states.

My $.02, have a great trip,
=Tod

Where are you flying into and out of? How many nights will you sleep in IT?

It's been several years since I was in the Cinque Terre but, as I remember, it was easier to get there from Florence than from Siena. Others will be clearer on that. 3 nights in Siena will give you a chance to do more than the main attractions. Renting a car would not be on my list of possibllities. There really is enough to enjoy in the medieval city. 3 nights means basically 2 1/2 days, the way I travel.
Sorrento is my 'go to' place to relax. Day trips to Pompeii, Capri, the Amalfi Coast are easy from Sorrento. From Siena I would take the bus (easier than the train) to Florence and then the Freccia train to Naples. You don't say when you will be traveling and that could help you decide how to get from Naples to Sorrento - boat or Circumvesuviana train. Happy planning! Remember: you deserve this!

Thank you for info. are starting in Milan, Belligio, Verona, Venice, Bologna, then on to Florence. I should have added, we will be spending 4 days in Sorrento (which will be the end of out trip) and flying home from Naples. We are thinking of hiring a driver for the duration in Sorrento as we want to go to Positano, Amalfi, Capri, Pompeii.

Given all the additional details of your trip I'd suggest you look into the northern Ligurian coast just above the CT as a potential place to stay. The towns run from Santa Margherita Ligure to Levanto going from more expensive and fancier to a bit more everyday as you work your way down the coast. SML is Portofino adjacent with all that implies but you can choose a more laidback place if you want to.

All the towns are connected by the train which you can take into CT and Levanto also hosts the coastal ferry to CT.

I personally like the south side of the La Spezia bay - San Terenzo, Lerici with the marina and little Tellaro but they require a bus from the train and - for being so close - do not offer easy access to CT. Lerici connects to Porto Venere - where you can get the ferry to CT - by ferry but the trips are infrequent. Otherwise you need to take the bus to La Spezia and then train or ferry to CT. The area is much more Italians at the beach for the summer rather than foreigners on vacation.

Getting from this area to Naples is still going to be a bit of a trek but since you have more time in Italy than I originally thought that's less of a big deal. Local train to Florence and then fast train to Naples and then either have a driver or take the train to Sorrento.

Have a great trip,
=Tod

We are thinking of hiring a driver for the duration in Sorrento as we
want to go to Positano, Amalfi, Capri, Pompeii.

Personally, I'd skip road transport and use the ferries except for Pompeii. That one is cheap and easy via commuter train (Circumvesuviana) from Sorrento. Combine Amalfi and Positano into a 1-day trip; there's little to do in Positano and it's most scenic seen from the water.

Day 1/night 1: arrival in Sorrento. Yes, it'll take you most of the day to get there from the CT
Day 2/night 2: Amalfi/Positano
Day 3/night 3: PompeiI & some extra hours in Sorrento
Day 4/night 4: Capri

Move to Naples sometime the next day prior to your flight. Maybe visit the archeological museum that day (as long as it's not a Tuesday)?

Unless your dates have changed, this trip is 9/30 - 10/24; flying into Milan and out of Naples?
Milan, Belligio (Bellagio?), Verona, Venice, Bologna, Florence, Siena, CT, Amalfi coast and back to Naples (you should stay there the night before your flight) is a lot to squeeze into the time you have, especially if the 30th and 24th are travel days. How long are you staying in Milan, Bellagio, Verona, Venice, Bologna?

I'd consider skipping the CT in favor of adding 1 more night to Florence + one somewhere else.

Regarding where to stay in Cinque Terre, we are staying in Manarola. A friend of mine stayed there last year, and she loved it. Less crowded than Rick's favorite, Vernazza. This will be our first trip there, so I don't have firsthand experience. La Spezia has a train station and a cruise port, so I'm not sure how enjoyable it would be to stay there.