Bus from Marco Polo Airport to Piazzale Roma?

get a ticket before getting on

Which bus, where to buy tickets, bags safe in lower storage area, etc.?

If you are planning to get a vaporetto pass (highly recommend a length of stay pass)
- you can add your bus ticket to/from airport to the pass and save a few euros
Buy at the airport tourist desk

Luggage will be safe I don’t believe the bus makes any other stops

Just follow the crowds and the signs. You’ll be fine.

The Airport Vaparetto was 15 Euros last time we were there. You have to pay to transfer to another vaparetto to get through the Grand Canal, and they're expensive to ride on.
We just caught a taxi, as the ride's just not that far.
If you need to find your hotel, GoogleMaps covers Venice even though there are no streets on the island.

It is 14 EUR for the combined bus plus vaporetto. It is a 75 minute ticket when travel must be completed. The No 5 bus is right outside the airport door and goes every 15 minutes. They are low-entry doors with open space in the middle for luggage.

The bus alone is 8 EUR and the vaporetto alone is 7.50 EUR.

Note that there are two different buses: the ATVO express bus (no stops between the airport and Piazzale Roma) and the ACTV #5 mentioned above - this is a local bus with stops, designed for locals not for tourists (though tourists are allowed to ride it). They both cost 8 euros. The ACTV #5 will take slightly longer as you might guess but will get you there too.

You can buy bus tickets for either bus at the airport stop - the two buses stop there not far from each other. There have always been helpers there at the stop helping tourists buy tickets both times I've taken the bus from here. It will be almost impossible to get on the wrong bus or not know where to go - they make it very easy, more than at almost any other airport I've arrived at. (Try arriving in Gdansk!)

You can buy your tickets from a machine inside the terminal or outside by the bus stop. They do take US credit cards - in May, I used my American chip and signature card (did not need to use my chip and PIN card). You could also buy the ticket in advance and print it out to take with you - I did that one year too, but I wished I hadn't. (I bought the ATVO ticket but that bus was late; meanwhile, the ACTV bus was departing a minute after I got there, so I waited longer for the ATVO bus, which got me there later).

Because the ATVO bus has no stops, you can feel pretty safe (I'd say) putting your bags on underneath as no one will be able to get to them once the bus pulls away until you get into Piazzale Roma.

And, as I recall, the ACTV bus is like a regular city bus with no luggage storage, so you'll have your bag(s) with you. Try not to let them take too much space, especially if people are standing.