These are some selected useful web-site
Public transportation: http://www.actv.it
City of Venice: http://www.comune.venezia.it
Venice airport: www.veniceairport.it
Port of Venice: http://www.port.venice.it
In case of high tide, that is very common from October to April, check the official web-site of the city of Venice that will give you any information about the level of the tide and do a small investment (15-20 euro) in a good pair of boot !