options for storing luggage and touring Venice after cruise

Our celebrity shore excursion from Venice to Padua ends at the Marco Polo airport in Venice at around 12:30 P.M. Our flight does not leave until 1900. Where can we store our luggage and should we go back to Venice with the Airport bus to do some more touring and then return by airport bus at around 1700 to make our 1900 flight.

Can you store luggage at the Marco Polo Airport in Venice and if so where is the luggage storage office? Does anyone know if the shore excursion bus could bring us back either to the port or to the Piazza le Roma ( where there is the airport bus terminal) and is there luggage storage either at Piazza le Roma at the bus terminal or at the cruise port?

Which option would be the best given the above facts?

Thanks so much.

Cowboy Jim