That makes it a lot easier to plan.
The best (and cheapest) way to travel around is using the water taxi's (like a public bus service on water).
There are local services (around the main islands) and then the services from the mainland to the islands.
You can buy a pass which includes unlimited travel on both. Much cheaper than paying for individual fares and much less trouble.
Cheaper if you buy it in advance online, and then you pick it up from one of their 'booths' - the most convenient of which is 200 feet from the luggage carousels at the airport.
If you need, I can find you the link to buy it direct (and not through some agency that charges fees) and I might have a voucher code also.
You get a map and guidebook with the pass and it includes entry to some of the attractions also (ie the state run ones).
If you do as I suggest and pick it up at the airport you can study it in your cabin before starting your 'tour'

You will do 50% water taxi and 50% walking.
The walking is nothing compared to what you do at your yard sales though
One end of the main island to the other is only about the same as walking from Mandalay Bay to Caesars.

If you browse any maps online - here are some 'clues':
Airport (San Marco) and Cruise Terminal (Mestre) are on mainland.
There are 3 main islands.
1. The 'City', which is connected by causeway to Mestre (and your choice of travel is water taxi, bus, train, taxi, ship tender)
2. Lido, which is basically just beaches and only open in middle of summer
3. Murano, which you have to get to by the water taxi from the City