Seeking suggestions for 10 day Italy, Austria,Germany, Switzerland Itinerary

Does the rental company know you are taking a car across the border? Are you familiar with Italy’s ZTL zone laws? Are you aware you need an autobahn (expressway) vignette in Austria? Furthermore, parking tends to be an issue when you get there.
A good day trip from Venice is Padua (Padova [30m]): https://www.trenitalia.com/en.html. If you go to Padua, buy tickets for the Scrovegni Chapel before leaving home.
Instead of renting a car take a direct train from Venice’s S. Lucia station to Verona’s Porta Nuova station (1h 15m). I would sleep in Verona a couple nights and take a day trip to Vicenza (30m).
There is a direct train from Verona Porta Nuova to Bolzano but do not sleep there. Instead sleep in the Dolomites. This is where the mountains are not Bolzano.
There is a direct train from Bolzano to Innsbruck (2h 15m). With nine nights stay in Italy the whole time because you’ll spend a full day trying to get back to Milan and it’s never fun when hauling luggage. Pack as light as possible to make your trip more enjoyable.

Are you aware you need an autobahn (expressway) vignette in Austria?

You need one for Switzerland as well.

If you do take the train instead, you can skip Milan because there are direct trains from Lugano to Malpensa Airport every hour.

Response to Mary Pat -
“Does the rental company know you are taking a car across the border?” The rental company asks for this information when you reserve the rental car.

“Are you familiar with Italy’s ZTL zone laws?” We have driven throughout Italy and are very familiar with all of the laws and rules of driving. We wouldn’t dream of driving anywhere without knowing the laws.

“Are you aware you need an autobahn (expressway) vignette in Austria?” Of course. We never plan a trip without doing the needed research. Vignettes are also required for other countries we’ll be driving through. We have researched stops where they can be purchased and have that information on file.

“Furthermore, parking tends to be an issue when you get there “ We research available parking for places we plan to visit..

“A good day trip from Venice is Padua (Padova [30m]): https://www.trenitalia.com/en.html. If you go to Padua, buy tickets for the Scrovegni Chapel before leaving home.
Instead of renting a car take a direct train from Venice’s S. Lucia station to Verona’s Porta Nuova station (1h 15m). I would sleep in Verona a couple nights and take a day trip to Vicenza (30m).
There is a direct train from Verona Porta Nuova to Bolzano but do not sleep there. Instead sleep in the Dolomites. This is where the mountains are not Bolzano.
There is a direct train from Bolzano to Innsbruck (2h 15m). With nine nights stay in Italy the whole time because you’ll spend a full day trying to get back to Milan and it’s never fun when hauling luggage. Pack as light as possible to make your trip more enjoyable.” We considered a stop in Padua but a friend who has traveled extensively in Italy suggested that Verona was preferred over Padua. Are you aware that the expense of renting a car in one country and returning it in another is prohibitively expensive? This is why we are renting in Venice and returning it to Milan Linate, our departing airport. We have taken trains in many parts of Europe but for this trip we have chosen to drive rather than take the train. I’m not sure what you’ve read or visited but Bolzano is the gateway to the Dolomites and many roads branch off from there to scenic drives through the Dolomites. We always travel with a Rick Steves carryon and his Eurobag as our personal item, regardless of the length of our trip.

I’d rather stay in Meersburg rather than Lindau. I haven’t been to Konstanz

I wouldn’t stay in Bolzano either. Yes, I’ve been there. The start of the Dolomites are roughly 45 minutes drive from here. I’d stay IN the Dolomites rather than way out on the outskirts and have to drive to see them. Val Gardena is ideal. The Gardena and Sella Passes start here.

Paul