Train pass

No pass, because most of these trips will require you to purchase separate seat reservations. These reservations are included when you just buy a ticket. Since you will likely know exactly when you need to travel, you can save a fair amount of money by buying nonrefundable tickets well in advance.

And regional trains are always the same price and dirt cheap, thank the Italian taxpayers.

Unless you will use a Eurail Pass in other countries, it is of no benefit in Italy.
Just purchase point to point tickets.

Your station names are:
Roma Termini
Firenze SM Novella
Venezia S Lucia

The above are all direct (no changes) fast trains

From Venice to CT- you will need the name of the town you are staying in.
Your journey from Venice to CT will likely be 2 changes- once in Florence then again in La Spezia (about 5-6 hours)

From CT- probably 2-3 changes-La Spezia to Pisa to Empoli to Siena

Use the official train site
https://www.trenitalia.com/content/tcom/en.html

cathy,

Some of the trains you'll be using on the routes you mentioned will be Regionale trains and no reservations are required (or possible) for those. Rail passes are not an especially good value for short Regionale trips. When using Regionale trains with locally purchased paper tickets, it's important to validate the ticket prior to boarding the train on the day of travel. Failure to do so can result in hefty fines!