Hi Jane and welcome to our community! You'd have to work out the individual costs of all the rail trips you plan to take in order to figure out what the most economical solution is. Generally speaking, it's probably more economical to travel with individual tickets if you plan to travel to various locations within Italy. Rail passes are usually most economical for people who want to travel throughout Europe.
If you'd like personal assistance to look at the different costs of rail journeys both individual tickets and passes, I'm going to tag our @Traveler Experience Team24 here and you can just comment directly in this thread if you'd like one of our agents to get in touch with you to work out your itinerary. Alternatively, you can reach out to them directly via email at email@example.com or by phone M-F 9 am to 5 pm ET 1 (877) 375-7245.
Hope this helps! Enjoy planning your travel to Italy!