Planning on Florence, Rome, Naples, and Athens, planning on three nights each, with trains connecting except for a flight from Naples to Athens. First time senior couple primarily interested in history--does this make sense?
Its certainly possible, and in a logical order. Just realize that 3 nights in each place does not mean 3 days in each place,since you will sacrifice half a day each time you move to another place. Given all there is to see and do in each of those places, I'd really recommend another day in each city, if that's a possibility for you.
That depends on your objective for the trip. If you just want to say that you have been to those places, then perhaps it makes sense.
If you want to really experience some of the things that those cities have to offer, then no it does not. For three nights in each place, the general rule of thumb is that equals two full days. You will spend precious vacation hours with packing, unpacking, checking in and checking out of hotels and traveling from place to place. Is that how you want to spend your time? At the very least I would recommend dropping Athens.
Welcome to the forum! Glad others said what I wanted to add about how little time your itinerary gives you in each place! Just out of curiosity when are you going & have you booked flights? l agree, it would be best to drop Athens. You could easily spend a week in Athens on another trip! If ancient history is your focus, I would skip Florence as well, it's really a mostly a Renaissance & Baroque city.
As history buffs you will be utterly awed by Rome & Naples! (Be sure to spend 1/2 a day at the MANN museum in Naples) plus hopefully a day or two exploring Pompeii & Herculaneum & Stabae. If you did stay longer, you could also visit Paestum, the Greek ruins further south of Pompeii by regional train. If you're only interested in the ruins, you could stay in Pompeii & do a reverse commute into Naples for the day, which is what we did. Here's our detailed TR - https://community.ricksteves.com/travel-forum/trip-reports/great-trip-to-pompeii-naples-over-new-years-december-26-january-2nd-2026
Good luck!
My frank thoughts - it's not enough time in any of these locations. Three nights is 2 full days and days of travel on either side. With the exception of Athens none of your travel is really long so you won't lose too much time to transportation but 2 full days in each of these cities will force you to make really hard choices in what to see.
In Florence will Accademia and Uffizi in one day and Duomo, museum and Pitti Palace on the other? That's a brutal schedule and leaves a bunch of things out. Rome will be even worse given it has a solid week of top tier historical content. RS has itineraries like "Florence on 1,2 or 3 days" with suggested sights and timings. I would study these and make a list of "must sees" in each city and seeing how many days you think you need in each place. Then potentially adjust your days in relation to what you actually want to see/do on the ground.
On practical matters Florence airport is smaller and can be hard to fly into but nearby Pisa is better connected while Bologna is only 30 minutes by fast train. All three airports are connected to the train station by a tram or some sort so airport > train station > Florence is an easy option.
From there Milan, Venice and Rome are all effectively about the same distance - about 2.5-3 hours. You don't say where you're flying from but assuming international flights you need to be realistic about how much onward travel you're prepared for on landing day. I fly from the west coast so we're not up for another 3 hours of logistics and tend to stay in whatever city land in overnight.
Naples to Athens is about 3 hours and the Naples airport is very close to downtown so that's an easy connection. I believe only Easyjet and Aegean do direct flights so compare the two - especially with luggage charges on budget airlines.
Once you have a plan buy whatever timed tickets you want for the days you'll be in each city so you don't waste time in line and you don't miss anything. Time and money restrictions will always lead to some hard choices. You will get good advice here but as first timers there will be learning curve but ultimately the only way to know is to go.
Have a great trip!
=Tod