Yes, as others have said, make Venice your first stop --- in addition to the obvious, it's one of the nicest places in the world to recover from jetlag and many hours of travel.
I have only two tiny additional thoughts, having taken both plane and train into and out of Venice. You'll have many more choices of flights (and it's probably cheaper) to fly into Milan and right away take the fast train to Venice, so do check that out. And, to me, it's just more fun to arrive by train because you exit the train in Venice and you are in a few moments and a few steps THERE, there with the Grand Canal smack in front of you. Arriving at the airport, you still have to take other transportation to actually get to Venice --- not a big problem, just not instant gratification.
Read up on how to take trains in Italy, and give yourselves extra time to move from one city to another, especially since it looks like from your previous questions that this may be your first trip to a country where you don't speak the language.
OK, one more thought. If you time it right, you can use the train travel to solve or minimize the problem of what to do between the time one hotel or apartment requires you to check out and the next one wants you to check in.