young couple's first time to Italy

These are the kinds of questions that will garner MANY different responses. But first time in Italy - and you're NOT seeing Venice?? There's no other place in the world like Venice.

Tuscany is not well served by public transport, and that's why you'll read LOTS of people complaining about getting caught by a speed camera or ZTL fines while in their rental vehicles - which they just HAD to have because they're spending time in Tuscany.

Sorrento is on the coast at the terminus of the Circumvesuviana which starts in Napoli Centrale.

Yes by all means be in Rome on the day of your departure. You don't want to be somewhere else in Italy and dependent on public transport to get back to Rome. Lots of transport strikes in Italy.

Personally I think Florence is overrated and full of Americans. Rome, Venice, Sorrento and rest of coast is where I would spend my time. But it's your trip, and you'll have to decide that for yourselves.

The Marozzi bus makes only a few other stops between Sorrento and Rome (not from Amalfi). Sorrento is the transport hub, which makes it a convenient home base.

Around Tuscany and Umbria, some hill towns that are on or near rail lines include Orvieto (very easy funicular up the hill from the station), or these with a short bus connection from the nearest train station: Assissi, Volterra, Cortona (among others!).

To Tim's comment, I don't see the issue skipping Venice. Of your 4 planned stops, I would not rate Venice ahead of any of them and have been to them all and Venice. So opinions differ for sure.

Florence is Tuscany and no towns will be close to the Amalfi Coast but I guess stay south of Florence and you will be fine.
I assume you mean a smaller town to see the countryside and hill towns.
Rental Cars not needed elsewhere but very nice to have in the Tuscan countryside, public transit is poor for the most part unless staying in one of the cities which are more city than countryside. Siena a city is south of Florence and beautiful though so an option for you if not renting a car, if renting a car we recently stayed in Pienza and love that area which is southern Tuscany so maybe as close as you would get to the Amalfi Coast (though still very far and not served well by public transit)

We took the bus you mention from Rome to Sorrento and enjoyed it, thought it was a better and cheaper option than the train which had stops/changes involved BUT it is not faster by any stretch. The time seemed more of a suggestion and our bus arrived very late. They made stops for friends, stops for coffee (twice I think). I would not chance the bus if needing to catch an airplane that same day!!! It was quite humorous to us, I think we were the only non-locals on board. Was easy to do and had plenty of storage for our luggage under the bus. Drops off/picks up in Sorrento right where the other buses go to the towns on the Amalfi Coast. The bus station in Rome is a bit out of the way for most though so keep that in mind compared to Termini.

I would change plans to avoid multiple changes of hotels.
Not sure how many nights you have on the ground (nights on the ground are what you should count) so I give some ranges.

Arrive Rome (likely in the morning or early pm).
Go straight to Florence upon landing (by train). You will be there a couple of hours later.
Florence: 4-5 nights (day trips to Tuscany small towns from Florence)
- train transfer from Florence to Naples by high speed train. Circumvesuviana to Sorrento. stay in Sorrento.-
Sorrento: 4-5 nights
- train transfer to Rome, via Naples. Or also bus transfer to Rome (Marozzi)
Rome: 3-5 nights (day trip to Orvieto if you have at least 4 nights in Rome).
Fly home.

Since you don't plan to rent cars, I suggest you visit Tuscany from Florence (Tuscany's capital), which is the region's transport hub.

I like Roberto's plan a lot. It involves fewer changes of accommodations which will provide more sightseeing time and less unpacking, packing up again, finding the hostels, checking in and out, etc. All that stuff eats time better spent having fun!

Yes, definitely stay in Rome on the night before your flight.

I'll also agree that Florence makes a very good base for day-tripping Tuscany to smaller towns without a vehicle. As well, we personally loved the city and never ran out of things to see over our 4.5 days there!

Thank you all for your very helpful replies!