Err - when are you planning to arrive in Venezia precisely?
According to an old Italian friend, she reckons the best time is mid/late October, well outside any festivals/school hols/events. Otherwise, spring & summertime, the whole place is absolutely infested with tourists these days. Cruise ships have added to the load, where they can spill thousands into the place, at once virtually. The place endured major flooding early this year & the authorities are looking at ways of bringing matters under control, rather as some ski-resorts do, in an attempt to limit numbers. Parking - easy to check out the garaging options near the road/rail causeway; just google it up.
Personally - we used Camping Fusina many times in the past. It's an easy boat ride into the old City but the Mozzis can get unbearable. Latterly, since the tourist boom, we have stayed out in Padova, using the Hotel Galileo, which has excellent underground parking. It's a short bus ride to the station (tickets from hotel reception), then a 30 min trip into Venezia on the train. Padova is well worth exploring itself though; a beautiful old City. Their is/was a great little restaurant not far from the HG, called El Funghi IIRC. Brilliant food & grog at sensible money, they cater for the Uni personnel.
Whatever you decide, enjoy the trip.