Itinerary second guessing

Rome deserves four nights and if you add a day trip to Pompeii make it five nights and forget Salerno. Because CT is the outlier skipping it is a good idea.
Florence deserves three nights and does not include day trips. If you add Siena make it four nights and take a direct bus (1h 15m) not a car.
Venice deserves three nights. With that said this itinerary requires twelve nights. How many nights will you be in IT?

Are your flights booked? When traveling to Italy, it's always best to fly INTO Venice and out of Rome - it's about how they time the flights in Venice and the Vaporetto schedule. So if you can fly into Venice and back home from Rome, it's usually easiest. Plus, it's usually easy to fly direct home from Rome

You can never have too much time in Venice. It's one of my favorite European cities. I find CT too crowded, others love it.

If you need good day trip recommendations from Florence - we loved WalkAboutFlorence - we did 2 of their tours - BEST OF TUSCANY and CHIANTI WINE & FOOD SAFARI.

Apologize for jumping back and forth for days and night, so Rome is 4 full days, 5 nights. Pompei is next and not going to change, Salerno for the night is because the train to Florence is direct and fastest. Realized our mistake leaving out of Venice after booking flights, but too late now. 16 nights in Italy.

I would skip the Cinque Terre this trip and add the 2 nights someplace else.

MTsumi, we flew roundtrip Venice last September. Our flight left Venice for home around 11:30am. We had no problems

Your gut is right. Drop the Cinque Terre if you are only giving it two nights. Venice deserves at least three nights and four are better. Those who don’t give it time tend to dislike it.

Venice deserves at least three nights and four are better.

Agree with above. It is truly a unique place and deserves even more nights if you can work it in.

You could stay in Naples rather than Salerno after visiting Pompeii. It would save a bit of time on the trip back north. I know some folks really are leery of Naples, but the archeologial museum is very good, and it has some of the best stuff found at Pompeii.

As to Naples, we are using all our time in Pompei viewing the sites with a nice evening in Salerno for dinner, maybe catch the passeggiata along the seafront. Really won't have time to visit anywhere else. The Salerno Italo is direct to Florence and the 40 minutes extra vs Naples is negated by our stay being 5 minutes from the train station.

What time does your flight depart Venice?
Rome five nights - this allows time for a day trip from the Roma Termini station to Orvieto (1h 15m) and then you’ll need to take a bus to reach the top of the town: https://www.trenitalia.com/en.html.
Salerno one night - then you’re taking the 1h 15m direct train from Rome’s Termini station to Naples Centrale station? You’ll need to follow the signs deposito bagagli (near platform two) which is the left luggage area.
You’ll then need to go underground at the Napoli Centrale station and get on the Circumvesuviana train to Pompeii: https://www.sorrentoinsider.com/en/naples-to-sorrento-train-schedule (45m). The train from Central Naples to Salerno takes 45m.
Florence four nights - the next day you’ll take a direct train from Salerno to Florence’s SM Novella station (3h 15m) for three nights. Buy tickets for the Uffizi Gallery two months out to guarantee a reservation.
A good day trip from Florence is Milan that takes 2h by direct train. There aren’t many of these direct trains but there is one that departs at 9:55a and returns at 6:10p. Reserve tickets for Leonardo Davinci’s The Last Supper before leaving home.
Siena two nights - take a direct bus to Siena (1h 15m) for two nights and sleep in the old town. Tour the duomo and Il Campo square your first day there. The next morning rent a car (get an early start) and get on the SR2 then turn left onto SP146 and stop in Pienza’s old town and then Montepulciano. This drive is full of luscious green rolling hills dotted with well-maintained farm houses, and possibly sunflowers if you're there in June and is an unforgettable scenic drive. This is why you go to Tuscany. At the end of the day return your car.
After two nights in Siena, take a bus or taxi to Siena’s train station to Venice’s S. Lucia station (end of line meaning when everyone gets off) that takes 4h 30m. This requires a change in Florence.
Venice three nights – I don’t agree you need more nights in Venice unless you’re planning a day off the lagoon. However, if you have an early morning departure you may want to spend your fourth night near Venice’s airport. Otherwise, expect to pay in the three digits to get from your hotel on the lagoon to the airport by water taxi. There is also a bus departing Piazzale Roma near the train station as early as 4:35a and takes 30m.
While in Venice, make sure you ride the vaporetto (water bus) from one end of the lagoon to the opposite at twilight. You won’t see the decay on the exterior of the palaces that line the Grand Canal, but you will see the ostentatious crystal chandeliers that illuminate their spacious foyers. The experience took me back in time. On your second day in Venice get lost.

Our flight leaves at 6:25 am. We booked the flight based off a travel agent itinerary then filled in the activities later. Agent quotes were $8000 more than we could book on our own. Realized Venice would have been better coming into after the fact. Our last night, we're staying at an airport hotel close enough to walk if needed.

Too bad about the early flight of Venice...but you'll survive, just an inconvenience you can't get out of now, so just plan for it. Live and learn.

I don't necessarily agree that you should skip the Cinque Terre, but I would understand why you would, because it is a bit out of the way. On my first visit to Italy (included Rome, Florence, Venice, and Pompeii), the Cinque Terre was the highlight! I know that makes me sound like a rube without much appreciation for history or culture...but I'm a photographer, and the views in the Cinque Terre are stunning. The hikes were memorable. (To be fair, I loved Venice too and have been back to it several times. Not to Florence. And although I didn't love Rome, the Roman ruins were amazing and did not disappoint.)

However, I first visited the Cinque Terre in 2007 when it had already been discovered by Americans but still wasn't quite the mob scene it has become. Corniglia is a beautiful town which will feel a little less overrun by tourists due to it's elevation above the train station (and no ferry stop), but doing anything during the day in the Cinque Terre in May/June will seem crowded. Just be prepared for that if you go. The evenings are much nicer.