I was planning to get some euros at the bank before arriving in Italy. For instance, to get to the hotel in Venice (our first stop) from the airport, would I pay the bus and vaporetto in euros?
Of course.
It's really a comfort level to have Euros when you land. But, you will pay your bank about 5% to buy them. Or, you can use the ATM at the airport. But, be cautious here as the ATMs in the airport of sometimes not bank ATMs. Instead, they are Travelex or some other type. The conversion rate is not that good. But, it will work to get you a few Euros until you get to a bank ATM. Or, you can use the money exchange place if they have one just to get a few Euros. We've done that in Canada, China, Mexico and other places just to get a few bills in the native currency.
If you want to save some money for a nice dinner in Venice, you could wait and use the ATM machines at the airport like we do. Just be careful in which ATM machine you use. Also, see: "Graffiti Wall > Money/Communication > ATMs: Minimizing Fees" for additional information.