I would pass on Venice and hit the roads down into Como.
Venice is well worth a couple of days if not more. There is a wealth of things to do and see. We never even try to go to Venice by car. I would recommend leaving the car in a secure garage somewhere and going by train; Santa Lucia station is very well placed as the starting point for visitors. There are parking stations but I have never investigated the cost or even if you have to book ahead.
In that area the city of Chioggia is well worth a visit and is less tourist oriented than Venice.
Highly recommended is a visit to Comacchio, sometimes refered to as "Little Venice". If there don't miss the museum,
Museo Delta Antico. One of the interesting exhibits is a Roman ship that was recovered, complete with cargo, after being burried in the mud for nearly 2000 years.
We find the whole Po Delta area fascinating and have visited it several times. Watch out for the speed cameras: I managed to get 3 fines for minor excess of speed on one trip

all for less than 5 km/h over the limit.