It depends on where you want to live, Italy is VERY diverse for a country its size (it used to be multiple countries not that long ago, after all). I'm from the north.
The average salary is about 24-34k€ depending on latitude, but roughly one third of that goes into paycheck taxes before you even see it. A skilled professional can make up to double that, but that's not easy, and only in the north, where life is more expensive. All of this is excluding places like Milan, where everything is WAY more expensive.

Internet connections are a shot in the dark in rural areas sometimes you can get 250mbit, sometimes 0, I know of people who work from home with 30Mbit connections and it's painful.
Rent depends strongly on the location and the city, a 80m^2^ apartment in a secondary city is probably 800-1200€/month right now, that is why most people live with their parents until they get a stable relationship, as you need two incomes to afford a place to live usually. I spend about 100-200€/week for groceries for two adults, but we both make good money and I tend to buy expensive stuff.

Air conditioning is painful. My home isn't super modern, so insulation is what it is, I probably spend 800€/year in the summer for A/C, and the machine itself is 2 years old, so it's an efficient one. The one I replaced was even more expensive to run.