I've been 5 times to Venice and used a 16-85mm lens on a Nikon D300S, and found it almost perfect 95% of the time.
The only reason I take my other lens, a 70-300mm, is because I have it.
I've used it a few times, but there were a couple of trips that I never used it at all. The streets and canals (Grand Canal aside and the channel between the main islands and Guidecca) are so narrow anything too telephoto will be a waste of time imho if one doesn't want to carry around loads of gear.
My usual tips for Venice is walk to see as much as possible. Buy a travel ticket, though expensive, when you find yourself lost, feet aching and on the far side from where you want to be/thought you were, a Vaporetto is a godsend. Getting lost is part of the fun though. You think you have a pretty good sense of direction until you start walking around Venice.
I like going on the Vaporetto too, some great views, and very relaxing. Try to get the seats at the front or at the back (depending on the design of the boats) by getting on at the start of a route.
Try not to spend money near St Mark's Square or Rialto Bridge.
A few minutes walk away and prices can be quite reasonable. I always stock up on drinks for walking at the supermarkets for a fraction of the prices in the small café's and shops around the city. Drink a lot because it will be scorchio. It was still hot when I have been in April and October, so should be a lot hotter now.
Great views from the bell towers in St Mark's Square and San Giorgio Maggiore.
I always go to Burano at least once a trip, as it is so colourful and photogenic. And though a bit long of a trip, it's a relaxing ride there and back.
I had planned to go there next week, but a broken camera has robbed me of my photo Mojo atm.
I will hopefully go there again when my new camera is repaired, and I have the money again.
If there is anything specific you'd like to know, ask, and if I can answer I will. Or someone else will I'm sure.
Bon Voyage.
Btw,
I looked on a webcam the other day and noticed that they haven't finished the restoration of the Rialto Bridge. Looks good without the hundreds of tourists who seem to spend all day on it, but there looks like a little bit of scaffold on the central arch at the top of the bridge. Hopefully they take that down pretty quickly.
Please let us know how it went.