Travel options in Italy - 4 days.

You can use the train to travel between the Italian cities. It is more convenient and efficient.

https://www.trenitalia.com/en.html

Since you're planning to visit Rome, Florence, Venice, individual train tickets will cost less than an Italian rail pass, especially if you buy tickets in advance and are able to get a discount.

Why not skip Rome and Just visit Florence and Venice. To fit in 3 cities in 4 days is very hectic and tiring.

I would discourage a car, as Italian city centers are all off limits to cars without resident permits. Just use the search box above and search "ZTL" to read all the horror tails of people who received tickets for cluelessly entering these zone where automatic cameras record you number plates and send you violation tickets, after getting your info from the car rental agency, which by the way, will charge your credit card about 30 or 40 EUR for each inquiry they get from the police. And that is before the actual ticket is sent. Also driving in bus lanes, speeding from robo cameras stationed all over the place.

Train tickets in Italy are cheap and easy. Local train tickets must be validated in the stamping box on the platform. Long distance trains have seat reservations which come with a purchased ticket, but have to be bought separately if traveling with a pass. Reservations cost 10 EUR per person per train for the fast trains.

There is also a competing high speed train company, Italotreno, that operates on the Padova-Florence-Rome-Venice routes that is often cheaper than the Freccia Trenitalia trains, and some say nicer. https://www.italotreno.it/en

I agree with the advice to omit Rome on this trip since you have such a short time. Enjoy Florence and, if you really want, another city on the same rail line such as Bologna.

You really don't want to spend each day checking out of a hotel, taking a two-hour train ride, and finding and checking into a hotel in a new city, with so few nights. You didn't mention the departure time on June 3, but it's risky to train a long distance the same day as a non-changeable international flight.

I know it seems disappointing, but you have a vast amount of Italy's beauty and wonder in the area. Besides Venice (where we slept four night on our first visit there ... ), you have Padua, Vicenza, Verona, Bologna, Mantua, Reggio Emilia, and more. (Do you know that the Venice Biennale of [contemporary] Art is currently open?) Now, Milan is not my favorite city in Italy, but ... if only you had left time to buy Last Supper tickets! And it's a lovely, historic city. Any chance you're flying Emirates, which uses Milan? What is the routing from Venice's airport?

Florence is a wonderful city if you are interested in Renaissance art, but is the whole party interested in art? Note that the Doge's summer mansion in Stra, Villa Pisani, is about as famous an art property as you can find outside Florence or Rome. And the number of actual Palladian villas in your neighborhood is astounding. There's plenty of good wine made in the Veneto.You're not in a bad place for three well-planned nights.

Too much for 4 days