My family and I, six in total, visited those cities in May.
First, let me tell you that if you take a water bottle, and I suggest you do, you will find public fountains that have drinking water in many piazzas. They are small, like our drinking fountains. Not the big fountains. Except in Roma, but more on that. It will be marked, "non potable" if it is not drinkable.
I will start in Milano. If you are there on a Saturday, I strongly suggest a neighborhood street market. It is located just north of Porta Garibaldi train station. Find Piazza Tito Minitti on Google maps. Via Pietro Borsieri. It just happens that the picture was taken when the market was set up. I suggest you visit the Duomo. Then wander the streets. If you leave the Duomo, and head NW up Via Dante, you will get to Piazza Castello. It is an medieval castle. Very cool.
Firenza was very nice! So many things to see. But, I suggest avoiding the very touristy market here. It is strictly for tourists. Visit the Porta Vecchio. Yeah, it for tourists, but you must see it. Visit both the Uffizi and the Accademia. go to the ticket office and buy your tickets ahead of time and avoid the line to get in. There is also a reproduction of The David in the Piazza Del Signoria. Well worth the visit. There are other statues there and another museum we did not visit, but I understand is well worth it. I also suggest the Garden di Boboli. If you cross the Ponte Vecchio, it is just up the road. Also visit the Duomo here. Pay the 8 euro and climb to the top of the dome. Be prepared for narrow stairs, but it is worth it.
Now off to Roma. Hit all the tourist spots. The Vatican, Spanish Steps, Trevi Fountain, The Coliseum, and the Forum. Near the Spanish Steps is a famous fountain that has spouts of drinking water. the water is carried from outside the city by aqueducts and is very good. I suggest buying the combined ticket for the Coliseum and the Forums. You will save money and again, avoid the line. We were only in Roma for 36 hrs. so we tried to make the most of it.
Here are a few thinks I learned about travel in Italia. Tipping at restaurants is not expected. Servers are paid a living wage. You have the table for as long as you wish. Cash is the way to go for purchases. and there is no tax on your purchases. Credit cards for hotels or big purchases. Be mindful of pickpockets. Get accustom to saying, "no, no, no" to the many panhandlers. There are also many persons trying to sell you things on the street, again, "no, no, no." My suggestion is that if you feel the need to help the poor, there are boxes in many duomos for donations to the poor. If it rains, EVERYONE, will try to sell you an umbrella. I don't know why, but Italians don't wear raincoats, they ALL use umbrellas. Without one, you are marked as a tourist. Be prepared to walk. all of the cities you are visiting are walkable. Especially, Firenza.
also, be on the watch for "stoppageo"?. (I'm not sure of spelling here.) there are day strikes of trains, or subways.
Finally, enjoy an "apertivo". This is a pre dinner "happy hour" at many restaurants. They provide free snacks while you have a nice drink. the popular ones are Spritz, and Negroni. Apertivo usually begins about 7 pm, 1900 hrs. In Europe they use a 24 hr. clock.
Thanks so much for the tips!! I've updated our itinerary