I've found my 16-85mm fine for Venice. I find that a perfect focal range for cities, so the kit lens should be good enough. I'd always want a DSLR though just in case there was 'the scene' you happened across. I also have my compact camera for snaps for memory's, which may not necessarily be any pics/videos I'd want to show anyone else.
If you plan to get out early take a tripod, though it depends on how early you plan to go out. I was there at the beginning of April last year and got out about 7ish (I think) in the morning. It was getting light, and it will be even lighter around that time early May, so depends on how early you plan to get up.
Obviously good for pics at night too, though you may not get the chance to get out at night.
Buy a travel pass while you're there to get you quickly to where you want to take pics of early, and if you go walking in general, makes it easier to get back to where you are staying if you find yourself on the wrong side of the island with aching feet. It is so easy to get lost there it's unreal.
Get away from St Mark's Square and the Rialto Bridge areas, and you can get away from 90% of the rest of the tourists and it's a more relaxing place.
The Vaporetto rides are part of the experience though. A boat trip along the Grand Canal is a must, you can either try and get at the front of on some of the boats, or sit on the outside at the back. The closer to the start of each route, the more chance you have of getting the best seats.
Three days is too short though to take pics of too much, especially if you are with a loved one. A day out to Burano is a nice trip, relaxing boat ride and lots of colourful buildings to see, and not as packed as St Mark's Square/Rialto Bridge. I find Burano much nicer than Murano photographically, though you can see some nice glass blowing demonstrations in Murano. Good views over the city from the bell towers in St Mark's Square and San Giorgio Maggiore.
Took me five trips to think I've had enough of Venice. (for now) Three days will just be a taster.