Fiumicino to Termini, what tickets to buy ahead of time

Don't pre-book train tickets until you know for sure that the flight is going to arrive on time.
If you take the Leonardo Express book it separate from Rome to Bologna.
If you were to arrive at FCO at 6:05 am you would make a 9:10 or 9:35 train from Roma Termini to Bologna in normal times.

1. --- Should be able to go through in an hour. BUT -- who knows what normal is these days. Once on a Sat morning about four years ago it took over 3 hrs to clear immigration. Just two officers working the mob. And they were not in a hurry.

2. Easiest is to walk out and grab a taxi -- fixed rate 48E to central Rome. I think the L Express ticket is 16E per person. Absolutely no need to pre-book LE to Termini -- one fixed price and no reservations. Buy the ticket when you there, get on, and find a seat or stand. Roughly two trains an hour. Careful, there is local train at the same station that is cheaper and takes longer. We made the mistake of getting on that train one time.

3. I would not buy a ticket till you are on the ground and at the train station. Even the basic tickets has limits on exchange -- I think the window is two hours after the train has left. (According to Dario - down thread - the actual window is one hour.) There is no reason to buy earlier. You could buy both tickets -- L Express and the ticket to Bologna -- at the ticket window in the airport. What happens if you plane is delayed or even cancelled? Buy the tickets when you get there.

Lets run a quick time line -- Plane scheduled to land at 6.05 but doesn't till 6.30. Now it is good day and you get through immigration and custom by 8.00 and are walking to the train station. A couple of minutes to buy the ticket but you just miss the 8.25 train so you need to wait for the 8.55 train. You are off the train at 9.30 walking to the front of the Termini. It is a bit of a hike as they bury the L Express in the far corner of the station. Should be able to catch the 10.00 train. Now did anyone what to use the restroom, freshen up a bit, catch a little breakfast somewhere, maybe buy some a little picnic lunch for the train, or do something else. Point I am trying to make is that you have a lot of time variables along the route that can cause delays and you may not be able to control it.

Take your time. You are on vacation. It is less stressful to wait 30 minutes for a train than running to catch one in five minutes.

No need to buy ahead, the train is like a subway, just show up, buy a ticket, either from a manned window or a machine, VALIDATE IT, then hop on the next train. Even at peak season, they are not packed. There are no reserved seats anyway.

There are only two trains that leave from FCO, but make sure you are getting on the Leonardo Express destination Termini.

As for Bologna, it depends on your level of risk. If time is king, then just go and buy tickets at Termini for the next train, may cost you more, but saves time. If cost is a concern, then you have to allow a healthy buffer. 2 hours to get through immigration and retrieve baggage, another hour to get to Termini, then another half hour to get to your train, maybe even err to the next train. The risk of buying ahead, is if you miss your train, you buy tickets at full price anyway.

Buying the Roma Termini-Bologna ticket in advance at the BASE fare has no advantages, but you run the risk of wasting your money if you arrive at the track more than one hour after the departure time.
I may be wrong, but I can see only problems with no real benefits. Or reasons.

Strictly speaking, in normal times there are three trains departing from FCO station: the FL1 to Trastevere and other secondary stations in Rome, the Leonardo Express to Roma Termini and the daily direct Freccia to Venice that calls at Rome, Florence and Bologna. In September this direct FCO-Bologna high speed train will be running again. I hope not, but If your flight was delayed and you haven't purchased in advance, you could take it at 13:53.

Thanks for the help. Frank, I appreciate the timeline, helps me mentally prepare for things not going quite perfectly! I do think that if seems will 'just miss' a Leonard Express we will just try to catch a taxi (to Termini not Bologna).

Unless things have changed, the taxi should be a flat rate. See https://www.rome.net/taxi

... I do think that if seems will 'just miss' a Leonard Express we will just try to catch a taxi.... No, if you miss the train just wait. It will be quicker than a taxi because you have to walk back to the front of the airport to the taxi starter. Don't accept a ride from someone who approaches you with an offer of a taxi. Taxis are tightly regulated and charge a flat fee (I think currently 48E) to central Rome. There will be a queue at the taxi line but it moves pretty quick. It could take more than 30 minutes to return to the taxi queue and your are dragging luggage. So sit and relax a bit. There is a tobacco shop across from the ticket window at the airport train station.