Are there lockers in the Rome Termini Station that will hold large suitcases? Can they be rented for multiple days in a row?
Nope, no lockers at the train stations in Italy. They removed them some time ago. What they now have is MUCH better. They have a staffed luggage storage area where they hold your luggage behind a counter. They have these services at many large train stations in Italy.
At Rome Termini, the line the check you luggage in can be quite long so expect a bit of traffic. Cost is about 3Euros a bag. I don't know how they work multiple days.