Absolutely agree with lim3:
that this is far too much, especially if you are attracted to the relaxing and romantic vibes of some of these cities.
In Venice the list of standard attractions is quite well-known and includes the Basilica, the Ducal Palace, Salute, Redentore, I Frari, the Accademia, or a show at La Fenice (if that’s your thing). However, the attractions are, in some ways, secondary to the whole sum total of this ridiculous, beautiful city that a bunch of people decided to build in a lagoon and that messes with your whole sense of space and time, especially if you are used to cars. Just walking around is an activity in and of itself.
HOWEVER, even a rabid Venice-lover like myself has to concede that the areas just off the Grand Canal/San Marco/Rialto/vaporetto to Murano ARE AWFUL during the day. They’re filled with day-trippers who are in a hurry to check things off, which is the worst way humanly possible to try and see Venice, IMO. You have to suck it up on at least one day so that you can do the Secret Itineraries tour of the Doge’s Palace and go inside San Marco but then spend the rest of your days on Burano, Torcello, Giudecca, Sant’Elena, the Lido, or anywhere else! These same areas that are intolerable during the day are usually lovely at night, which is why one ought never to try and save money by staying in a hotel in Mestre on the mainland!
Gondolas–expensive, but (just IMO) if done in a quiet area of the city, a lovely experience. I have a marked personal preference for the Santa Croce/San Polo/Dorsoduro side as opposed to the San Marco side. I prefer to simply walk through Santa Croce toward San Polo until I find a little grouping of gondoliers (consider getting off the #1 vaporetto at San Stae and heading more or less to the left of the church–walking in that direction will take you toward San Polo sestiere).
Cultural note–As is the tendency in a lot of the northern regions of Italy, like the Piedmont and parts of Lombardy, Venetians tend to be more on the reserved side. However, if you show the *slightest* interest in learning more about Venetian-specific food, history, etc., most people will warm up considerably.