I need help with 2 things. Where do I buy local train ticket from Naples to Sorrento? At station or somewhere online?

I figured out the best way to get from Florence to Naples to Sorento to Positano

HOWEVER need to know how to get from Positano to Rome for a 5 pm flight

You get the tickets to the Circumvesuviana in the train station. It's more like a subway than a train, so they don't sell out or anything.

Don't know about Positano to Rome.

Circumvesuviana is a commuter train. You buy a cheap ticket from a ticket window to go through the turnstyle. It runs at the lower level of the same Napoli Centrale station.

For Positano to Rome, do you realize that when you traveled from Florence to Positano, your route was Florence-Rome-Napoli-Sorrento-Positano. If you reverse the order and use the same travel time and get off at Rome, you get estimate of how long it takes to Rome Termini. From Rome Termini, it is another 20-30min to switch the train from Napoli to train to the airport then 32 min train ride to the airport.

If you are traveling during busy tourist season in Positano, then you need to make sure you don't get caught in traffic traveling from Positano to the Naples train station. Best thing to do is figure out which train you need to catch in Naples to make sure you arrive at FCO by 2pm, and then pre-arrange for a driver to take you from Positano to Naples. Leave it up to the driver to tell you when he/she will pick up to get you to the train station on time.

Positano dp 8.45 - Sorrento 9.45/10.37 - Napoli PG 11.43/12.00 - Roma T 13.05/13.20 - FCO ar 13.52
Timetables may change at any time

Best is to be in Rome the night before your flight IME - strikes in Italy are not uncommon - you could be stranded in Positano, not that that is all bad. Strikes are previewed however so keep up on it and if you see one coming change plans.

another way to reach Rome from Positano is via taking a boat or bus to Salerno, which has direct trains to Rome - avoiding the dumpy slow CircumVesuviana trains and changing in Naples. May take a bit longer but an alternate route.

"another way to reach Rome from Positano is via taking a boat or bus to Salerno"
... with departure at Positano at 6.10am (if you don't want to risk to miss either the connecting bus at Amalfi or the train at Salerno).
BTW: I checked both solutions before posting

WATCH YOUR BELONGINGS ON THE CIRCUMVESUVIANA LINE. There is at least one pickpocket in every car. Be especially careful when you are about to get off the train, as that is when they strike, when you are gathering your luggage and getting ready to get off.

The pickpockets are experts at looking sleepy, relaxed, and completely innocuous. If you see somebody who looks like that, stare them right in the eye and memorize their looks.

Sew up your pockets before you get on that train. I'm completely serious. These days I hire a car to take me between Naples and Sorrento rather than take the Circumvesuviana. Or you can take one of the ferries.

the State Department ondce issued a warning about the thefts on the Circumvesuviana trains - that was some years ago but seems relevant now. One time I was on the train folk were shooting up in the back of my car - this is a poor area with lots of drug addicts - translates to thefts to feed habits.

But I've taken the train several times and have seen no other problems but yes be vigilant - tourists are targets because they are presum4ed to be wealthy.

I've never encountered pickpockets on the Circumvesuviana, but they can exist in any crowded place that attracts tourists. Like any crowded public transport in any city (including US). I have talked with people that were pickpocketed in the Naples train station.

>>>another way to reach Rome from Positano is via taking a boat or bus to Salerno, which has direct trains to Rome - avoiding the dumpy slow CircumVesuviana trains and changing in Naples. May take a bit longer but an alternate route.<<<

It's unlikely this would be any faster as Salerno is an hour by fast train past Naples. Ferries don't run often and don't put into Positano if the sea is choppy so it's possible you would have to take a bus, change in Amalfi.

If your trip itinerary includes Rome, then you need to rearrange your schedule to end your trip in Rome.

I guess I got cheated out my full tourist experience when I took the Circumvesuviana because I didn't get a pickpocket on my car. All I got was a bunch of old Italians, couples in their 70s and 80s, and the rest of us tourists. And everbody looked sleepy, relaxed and completely innocuous -- except for one sweaty guy who kept looking around, freaked out, breathing heavily -- but he was an American.

The Circumvesuviana is a commuter train. Like the New York City subway, you should watch your belongings because: You should watch your belongings.

You should not keep valuables in your pockets when you travel, even if your pockets are sewn up. Some men sew up their pockets when they travel to Italy to keep themselves from constantly grabbing their genitals, because it is against the law in certain parts of Italy, so maybe that is what disambiguous is trying to tell you. In a private car, you can do whatever you like inside your pockets.

How could that be against the law, sandralist? In what part of Italy? "Toccando le palle" is a protection against malfortune. I once read that the custom dates from Roman times. You don't need pockets to do it, either.

An Italian woman once told me, "If you don't have any of your own, you can touch somebody else's."