hey hey Kim L
where are you staying in venice and how many people?
europeforvisitors.com/venice
few parking garages are:
piazzale roma has a parking garage when you reach island as shoeflyer mentions
on the mainland are: mestre, marghera, and marco polo airport. read up on what they offer, the prices that are charged, is there a shuttle to venice, size of car to fit in stall and if covered.
venice-guide.com
parking in venice
make sure you have and IDP (AAA.com/IDP) for all drivers.
check into hotels are usually 2-4pm and check out 10-11am, keep that in mind unless you can get early check in, check with hotel. or have hotel hold your bags until check in
hope all works out for you, good luck
aloha