Nice..
I carry very little cash if I am in big cities. I have a credit card that does not charge an exchange fee, and a debit card. So I can get cash at the atm if need be.. harder in rural towns.. also if you carry a pack, keep your expensive stuff inaccessible from the outside pockets..Some Italians are very good theives. You won't even know they hit you.. zipper pockets keep your phone and wallet in front pockets. Wear sturdy material, because they will cut the bottom of the pocket out while you are walking along.. Language is not a problem in the big cities.. but the locals will cut you a breaking you at least try to learn a few phrases BEFORE you step on the plane..
In Venice the boats work like the subway.. take it to Lido and rent a bike. Ride to the beach.. Anything you want to see in Italy, reserve early. You need reservations to see museums and they are often booked way in advance.. if you want to climb the tower in the Duomo book it ahead..
Stay in air bnb , ( super hosts with good ratings) it is way better experience..
Take a guided tour in Rome on an e-bike. 3 hours will barely be enough.. it's an awesome experience.
Spend a day ( and a night ) in Tivoli!
Drink lots of water. Italy is hot. Take a hat.. and not a damn baseball cap.
Walking around alone is a bad idea. There are very sophisticated panhandlers, and in some areas you can wander into a crowd of them. They can make it difficult for you. If you can arrange to meet up with friends, that's a better plan.. there are these online language web sites where local speakers help you learn.. might be a way to get to know someone a little.. you can ask your airbnb hosts for tips about stuff also.. they are usually pretty helpful..
And be prepared to walk... a lot. Uber is expensive. Subway in Rome is not useful. Rome is seven cities built one upon the other. So the subway underground is not practical around the old city.. Wear sturdy shoes. You will be walking on cobblestones.. I wore keenes hiking low tops..
There are two dinner times. One around 5 for the tourist food like pizza, and the other after7 for actual Italian food.. you have to time it, because lunch is available for a window and if you miss it, you go hungry.
They serve a lot of food. My wife and I split a lot, so that helped.
Try to have some Bulgheri wine.. Yum!
Trains are good, but you can get fleeced, someone will greet you when you come in and show you how to manage the trains.. then expect to be paid. There are actual free greeters, but they are always wearing uniforms.. buy the air-conditioned seat, you won't regret it.
Renting a car in Italy was a terrible idea. Super expensive, parking is a nightmare, you can't see shit from the highway.. it looks like it might be a pretty drive down the coast from Venice, but it's just a concrete view.. Take the train..
Spain was super cheap when I was there last.. language is more of a problem than Italy, but that may have been because I was in a smaller city. (San Luca de Barramedos , I think.. where columbus and Magellan set sail from)
Any way, relax and have fun..
Rocks..