Possible Northern Italy Itinerary

The mosaics are truly stunning. Aside from the mosaics, the historic part of Ravenna is just gorgeous, and when I was there in July 2015, there were very few other tourists about. I think you'll love the place.

I also like Padua, which has quite a lot of sights to visit as well as an historic area that's fun just to wander around, though I guess it's not as drop-dead gorgeous as Ravenna's. If you're interested in the Scrovegni Chapel (which is very impressive), note that reservations must be made in advance, not on the day of the desired visit.

What is your plan in Bolzano? It's another town with a very handsome historic center, plus it has some museums--the major one for most foreign visitors being the home of the Iceman. But most people who go there are heading for the Dolomites, and the usual recommendation on this forum is to stay up in the mountains (perhaps in Ortisei) rather than down in the valley. I think the Bolzano weather should be generally OK in May; in mid-summer it can be surprisingly (to me) hot down in that valley, which is a problem if you don't have air conditioning in your hotel room.

No comment on Verona because I haven't been there; I chose Vicenza instead, which is also a good stop. I hope to catch Verona next time.

Ravenna is wonderful, but you can see it in one day. What do you plan to see in Bolzano?
Verona, we did the city in one day also.
Lake Como is very scenic, nothing wrong with that, but my preferences on going to Italy is about history, art, culture. Your trip leans heavily on the scenic.

I've been to all the places on your list and you won't regret spending time in any of them. I personally don't mind short stays (1-3 nights) especially if you travel light and choose hotels sort of near the train stations (between the station and the center, usually can walk to the hotel, not need to bother with taxis, etc.). But sometimes I prefer longer stays with day trips and a few of your places could be combined. For example, since you have already been to Venice maybe you could just revisit it as a day trip from Padua. Usually a day trip to Venice would be bad as Venice is best early and later in the day. But it's only a half hour frequent train from Padua and trains are all day long so you could still do that (be there early or late). I have also done Verona as a day trip from Padua, but I do think there is enough in each to warrant staying in them. I thought the mosaics in Ravenna were fabulous but of all the towns listed that was my least favorite, and it's an easy day trip from Bologna so perhaps save it to combine with a trip there some day. However, it's only 2 and a half hours from Padua so a possible day trip

I did use Bolzano as a base for the Dolomites (had a car that trip) but I loved the town itself. You can also see a bit of the Dolomites (not the best part, but still great) right from the center of Bolzano, there are a couple of cable cars from the center. From Bolzano do a day trip to Trento, another great city (but we were happy with a day trip there). I've also done Lake Como as a day trip from Milan and enjoyed it (also went for a couple nights on another trip) and by the end of a trip you might want to just base for a few days in Milan and do it as a day trip, very easy to train from Milan to Varenna.

If it were me I might do Padua 5 nights with possible day trips to Venice, Ravenna and Vicenza. Then Verona 3 nights with possible day trip to Mantua. Then Bolzano for 3 nights with day trip to Trento. Then Milan 4 nights with day trips to Varenna and possibly also Bergamo and/or Lugano (or Pavia).

Here's my Italy photos of all those places - https://andiamo.zenfolio.com/f739967755

Thanks for your helpful responses. In many ways I think I cannot go wrong here, as northern Italy is undiscovered country for me outside of Venice. Rick says that the hiking season in the Dolomites starts in mid-June, so I was not especially expecting to do much hiking. But with three nights in Bolzano, if the weather is right it could be possible. I could also see forgetting Como and visiting Milan for a day trip before ending in Florence again. Isabel, your photos make me want to move to Italy, not just visit.

I hate to complicate your planning even further, but look into Ferrara also (easy as a day trip from Padova).

I've been to all the places on your list (on various different trips). All are worthwhile, and other than Venice and Verona, not very touristed. I agree that I wouldn't worry about 1 night stops, particularly if your research doesn't turn up lots of designated "sights" in a place that interest you.

Definitely keep at least some time in Milan. As long as you're prepared for it not to be like the "Italy" that US visitors want or expect, there's lots to see and do there. As someone who also liked Madrid (not better than Barcelona, but in its own way, just as much), I think you'll enjoy your time there. While it's big, the efficiency of the metro means that getting around Milan is actually easier than in many smaller Italian cities.