Northern Italy

I don't know how the transport logistics will affect the order (try RometoRio to get a sense), but I would want at least three full days (so four nights) each for Lake Como and the Dolomites (check weather or the latter, and look up the best base for using public transport), as well as for Venice and Florence. For Siena and Cinque Terre, at least three nights for two full days. Milan could be a night. All of this is fairly meaningless without knowing what you want to see and do in each place, but hopefully this bare bones sketch is useful.
Much will depend on your interests, how much time you have, and where you depart.

Rome2Rio

How many nights do you have left on your trip? Into what airport did you fly from home?

You're really going to have a hard time seeing the Dolomites without a car. I'd skip it and just go to the other cities. Many fly out of Pisa (1 hr. west of Florence by local train) to large gateway European cities. Or, you could back track to Milan if you can catch a direct flight home.

Thanks! I am not looking for a planned out itinerary, just your thoughts on what YOU would do, how YOU would lay it out. Don't worry so much about exactly what we want to see, I'd like to see ideas based on what you all like. We have learned so much in the past from people sharing thier ideas, not what they think we might like. We also don't have a certain amount of "time left". We will figure that out when we make final decisions on what tot see. FYI - we will be plying home from Italy to Portland, OR

Valadelphia - thank you for your thoughts on hoe long you would stay places!!
David - thanks for your thoughts on the Dolomites

Lugano to Milan is 1 hour by train, from there another 1 hour to Varenna on Lake Como. I've done a day trip from Milan to Varenna and the 'mid lake' villages and it was "OK" but at least one overnight would be better. So I'd probably go from Lugano, via Milan to Varenna and spend 1-2 nights.

Then I'd go from Varenna (again, via Milan but not stop) to Venice and spend minimum 3 nights (which will give you just over 2 full days). I agree that the Dolomites without a car is difficult, if you are coming from Switzerland maybe you could skip it. But if you do want to do it anyway you should give it a minimum of 3-4 nights since you will spend most of a day getting to and another getting from.

Then Florence and Siena. Those certainly 'deserve' at least one overnight each but can be done together (base in Florence and do Sienna by bus as a day trip). Minimum 4 nights for both of them.

Then Cinque Terre - two nights so one full day is minimum.

Then back to Milan for two nights so one full day before flying out of Milan.

So 12-14 nights would be my minimum to cover all those places. Obviously you could easily double that, but if you are 'active' and like a relatively fast pace that would be an enjoyable trip.

isabel - Thank you for your reply!! Wonderful info to consider!!!

Flying home to Portland, OR

I'd also be happy seeing the Dolomites from a distance. I just think they are amazing :)

Some people who frequent forums like to just say what they did and offer it up for informative purposes, and often that has its place.
Some of us like to delve into what the traveler's own goals are because we passionately believe that is what makes travel work well, tailoring it to personal interests--so that is why these kind of questions get push-back. Say someone had some special reason to spend time in Milan. It gives me pause to say one night, even though that is my own honest answer. Do consider fleshing out what you want to see in each place--it makes for richer feedback in the end! Or for example, you just want to pass through Florence to see one thing? There is no right answer to these questions without knowing a lot more about you and what you want to see.

valadelphia - Exactly!!! This is just our jumping of point! As we start to consider options, explore the travel guides, online info, and others thoughts (hence this post), we will be back with more pointed questions. Thank you :)

If it were me and time was unlimited, I would:

Fly into Milan, spend 4 nights
Lake Como, 3 nights
Dolomites, 2 nights
Venice, 3 nights
Cinque Terre, 3 nights
Siena, 3 nights
Florence, 4 nights
Fly home from Florence

Now if you only have 7 nights on the ground? I would do: (i have already been to Venice and Florence out of your list)

Option 1: Fly into Florence
Florence 4 nights (Day trip to Lucca and Pisa one day, Day trip to Siena one day. Two full days in Florence)
Train to CT, 2 nights
Train back to Florence, 1 night
Fly home.

Option 2: Fly into Milan
3 nights in Milan (possible day trip to lake area)
Train to CT
2 Nights in CT (one hike day and one relax day)
Train to Florence
2 Nights in Florence (museum day and maybe day trip to Pisa/Lucca or Siena)
Fly home from Florence.

Did you fly to Europe from Portland? What was the initial stop? This important to know with respect as to how to get home.

On www.skyscanner.com, IT to Portland, it would seem the best option would be Milan [MXP]. You could check multi city from the airport you flied into; or go back there for a round trip.

You’re carrying backpacks, where you would not want to store your passports [copies in a separate location], CC’s and debit cards. Those should be secured under your clothing or else out of reach.

The other portion of out trip is......
Flying from Portland, OR to London - 4 days with friends
Fly from London to Basel, Switzerland - 1 week with son and DIL in Kandern, Germany
Basel to Zurich - 1 night
Bernina Express from Zurich to Lake Como area (maybe a night's stay along the way)
Time in Italy
Fly home from Italy to Portland, OR

This is our 3rd trip to visit them, but our first time to Italy. Last trips were backpacking though Germany, Netherlands, Belgium and France.

Since you are coming from Switzerland and Lugano I'd skip the Dolomites and really if you spend time on the lake there even Lake Como will seem way too similar. Nothing to see in Milan IMO. I see two options w

CT - 2 nights
Siena - 1 night since it's quite amazing to be there in the evening sitting on the square
Florence 4 nights and fly out from there if you can

But I could also see
Lake Como
Dolomites
Venice

I agree with most of the advice already offered, but since you asked about other places, there are three interesting towns along the rail line between Venice and Milan: Padua, Vicenza and Verona. I haven't been to Verona yet, but there is enough in Padua to justify spending at least a couple of nights there. The Duomo aside, I would prefer Padua to Milan; I have no interest in The Last Supper.

Another possibility is the hill town of Bergamo, which can be seen as a day-trip from Milan.

I'm convinced that Turin is wonderful (there seems universal agreement that it's more attractive than Milan), but I can't give it a personal recommendation yet.

If I had limited time, I'd be inclined to stick to the stretch of Italy between Turin and Venice on this trip, planning to hit Florence/Siena/Cinque Terre on the next trip. That would allow you some time in less touristy places.

I liked the Dolomites a lot, but I'm not sure about hiking conditions at the time of your trip. I think of that area as winter for skiing/summer for hiking. I'm not sure how much of the mountain transportation will be operating in late April/early May. I assume the buses from Bolzano and Bressanone will be running just fine to places like Ortisei, but to get up above the villages may be a challenge.

For the Dolmites Peek, take the train from Milan to Trento [about 2.5 hours, change in Verona], a delightful town. Stay at the Grand Hotel, everything first rate, including the bar and the breakfast; rates surprisingly low. Lunch and dinners at the Antica Trattoria due Mori, one of our top five in Italy. After lunch ride the cable car.

Next day take the train for an excursion in Bolzano [50 minute], including a cable car ride:

https://www.ritten.com/en/highplateau/highlight/cablecar.html

Venice next.

I'm agreeing with others who suggest you save the Dolomites for another trip. We were there in mid-May and it was very much shoulder-season. Not much was going on and the Alpe di Siuisi mooshy expanse of slush. The cable car up there wasn't running and we needed a car to get there. Also, it was cloudy for our three days there, and we never got a clear view of any mountain peaks. I'm looking forward to returning at a sunnier time of year!

Nikelini - thank you for your thoughts!! I didn’t even think about the possibility of it being cloudy!! I think we are going to save it for another trip!