Most places are used to tourists, so really, anything goes, they won't kick you out or beat you.
Some points to make though.
As someone else alluded to, the afternoon meal (lunch I suppose, but eaten at 1:00 (13:00)) tends to be a bigger heavier meal traditionally, then lighter in the evening, but again, tourism sees the evening meal as heavy anymore.
When my wife and I eat (she does not eat meat, but will do seafood) we always start with a bottle of water (we prefer sparkling) it is almost expected that you will have a bottle of water, look around, every table will have one, except for the few Americans who practiced "Tap water, Please" in Italian. We do get wine, either by the glass, but usually a bottle, if they have a house wine in a carafe, that is usually a cheap, quality option. You can pass on wine, with only a sidewise glance from the waiter.
We always get a starter, an Antipasti to share. I think some of the tastiest, more unusual things can be found there.
Then, we usually each get our own main, we have shared, but portions tend to be right sized, I like meat, wife not, so she usually gets a pasta, I get whatever sounds good. We have never each ordered both a Primi and a Secondo, though I might myself on occasion. (I have seen rail thin Italian women though order an antipasti, a pasta, and follow it up with a steak, and dessert)
Do not overlook side dishes (Contorno) usually a great plate of fresh seasonal vegetables.
Then we flip a coin on dessert, a walk and a gelato is preferred, but if they have something interesting, then yeah.
Probably the other look you will get is if you decline coffee at the end. I rarely can do caffeine late at night, so I do decline usually, but I save face by ordering an Amaro, a digestif, there are a wide array of liquors to try.
All this will easily take an hour, with practice, two, no hurry.
I will add though, the more upscale the restaurant, the more the expectation you will do the above. a simple Osteria, or even Trattoria, less will not bat an eye.
The only other "rule" to adhere to is that a pizza is a single serving meal...proposing splitting one will raise some eyebrows.