Car Rental/Train HELP for Rome/Cinque Terre/Tuscany

Use Trenitalia .com
Put in Roma Fiumicino and your destination in CT

https://www.trenitalia.com/content/tcom/en.html

You can pick up car in La Spezia

Orvieto only has Hertz so you would be limited to that agency
You could drop the car in Rome or at Rome airport instead

Make sure all drivers have an IDP and do your homework on driving in Italy

There are many threads here about driving in Italy and how/ where to pick up/ drop off car
Do some forum searches, use the filters for Type and Date

To rent a car near the Cinque Terre the best option is La Spezia. Most agencies are at the cruise port.
If you pick up on Saturday afternoon or Sunday/Holiday the La Spezia offices are likely closed, so your best bet is the Pisa Airport, a bit further south along the coast.
To return the car before going to Rome depends on where you are coming from, but if you are going to Rome, then you might as well return it in Rome.
If you return to Rome just to catch the flight home and basically intend to spend only your last night in Rome, then I'd return the car at the airport and stay at an airport hotel.
If you plan to stay and visit Rome for a few nights and want to stay downtown, then you might want to return the car in the city.
All major companies keep multiple offices in the city of Rome, so which one to return the car depends on the car company you select.
check pricing here:
www.autoeurope.com
Pick Up LA SPEZIA ALL LOCATIONS
Drop Off ROME ALL LOCATIONS

Thank you!