Todi to Sorrento

You will need to take Trenitalia trains to Napoli Centrale and a Circumvesuviana commuter train from there to Sorrento. According to trenitalia.com, your route will be Todi Ponte Rio - Terni - Roma Termini - Napoli Centrale. For complete timetables that include regional trains, enter 20 October rather than 27 October. Information for regional trains only appears up to seven days in advance. Circumvesuviana trains depart from the lower level of Napoli Centrale. They run at least twice/hour and the ride takes just over one hour.

Thanks. This is very helpful. Please let me know if I am on the right track here. - First train from Todi to Terni. - Second train from Terni to Rome Termini. - Third train from Rome to Naples Centrale.
- Fourth (and final!)train from Naples to Sorrento. Also, if available, should I make reservations? Is second class the way to go? Finally, I will have a small suitcase and a carry on. Do the trains have a luggage area or do they stay with me? Thanks again.

Your Terni-Roma Termini and Roma Termini-Napoli Centrale have Frecciarossa and Intercity options (there is a third option but you have to change trains in Orte between Terni and Roma). You will need a reservation for these two types of trains (you can buy the ticket online, which locks you into a specific train and date, or buy the ticket in Todi; you'll still be locked in but you'll have more time to plan once you are in Italy). Fare is about 55 euro, travel time is about 3 hours, with change of trains for the faster option. There is luggage storage overhead which should accommodate your stuff, or a space between the pairs of seats facing away from each other that will hold a carryon. The Circumvesuviana has some overhead storage as well. By the way, Napoli Centrale and Porta Garibaldi refer to the same station.

Thanks!

IMO, 1st class isn't worth the extra money. All you get is 2 + 1 seating rather than 2 + 2 seating. Leg room is fine in 2nd class. Were you able to decipher the timetables on trenitalia.com?

Yes, I figured them out and have selected the trains to take. Thanks for the advice about the class to take.

The main advantage I've found in first class is that the cars, in my experience, have been less crowded, which makes it easier to keep my luggage at my feet. I'm short, and the overhead racks are much higher than on planes. I've had men put my luggage up, but I can't reach high enough to get it down. I also find that 1st class can be a little more appealing late in a long trip, if I'm tired and want extra comfort.