I am travelling to Italy in May and, when I land, have 1hr. 45mins. to get to Termini to catch a train to Florence. Is this enough time? I'm not checking any bags, just going straight from the plane to the Leonardo Express to Termini and then to my train to Florence.
You may just be able to make the connection but it sounds too close. There is a train every 30 minutes which takes 35 minutes to get to the Termini. Even with a best case scenario, it is cutting close. Plus if for any reason your flight is delayed then you will miss the connection.
There are several trains to Florence and unless you are taking an ESI which requires a reservation, you could hop on the first available IC train as soon as you get to the Termini.
Buy your ticket to Florence at the airport when you buy your ticket for the Leonardo Express. That way you'll know exactly which train you'll be able to catch at Termini. And you won't have to stand in line at Termini.