there will be no problems in Venice if you will place your tripod in the ancient and NARROW streets until you will block the passages of pedestrians, cats and pigeons, at that time you will have complains from the Venexiani, gatti e piccioni and at the end from Municipal Guards.
If you will be in the main place of Venezia you have to be careful of tourists flux and not to be an obstacle, in doubt ask to the security force.
It is forbidden to put down the tripod in churches, museums and others interiors, except for a private house in which you can ask the permission.
Last suggestions try to avoid the main touristic places they are crowded, best to visit them at the dawn or the dusk of a grey and foggy day. Some interesting places are in the islands surraunding the town: Torcello, Burano, Lido with the Jewish cemetery and Malamocco.
I invite you to ask for Venetian foods and dishes you will be satisfied......
If you need some specifications ask.