Any information on travel by train to airport in Rome would be helpful. Need to catch a flight at 12:00 noon on a Saturday.
Check Trenitalia website for schedules and fares. Fast train from Napoli Centrale to Roma Termini, 1.25 hours, departs nearly every hour. At Termini, Leonardo Express departs from track 24 every 30 minutes, takes about 30 minutes to get to the airport, then a circuitous path to international gates.
LE is a separate ticket, remember to validate it.
There are several train connections that can get you to the airport by 10:00, but don't cut it too close, in case of unexpected delays. Plan to leave by 6:00. If you miss your flight, the airline has no responsibility to put you on another one.
You must allow at least 3 hours once in FCO due to the T3 terminal. If you train from Termini to the airport, you will need to
board a shuttle bus with your luggage and go to a customs/clearing terminal, then return to the main terminal prior to boarding. It isn't difficult and the signage is great, it just takes extra time.