What kind of visa do I need if I want to step outside the airport in Italy on my lay over?

You will need a Schengen visa for tourist purposes, even it is just for 5 hours. So I would better stay within the transit area of the airport. A layover of 5 hours is not much, the plane might be late, you might have to queue at customs. Your connecting flight might depart from the very far other end of the terminal and you would have to check in and go through customs again. Don't take that stress, just relax in the transit area, do some shopping or have a drink. May be for your next vacation you plan a longer stay in Schengen countries, so that the visa fee of 35,00 € pays off.