How easy is it to fly into Florence vs. Rome? If you are connecting in Europe anyway and taking a connecting flight to Rome or Florence and the times are about the same, costs are about the same...absolutely, fly into Florence if you are starting your trip there. Don't break up your Rome trip into two separate segments. Do it as one visit to Rome, not two.

If you find it's easy to fly directly into to Rome and a lot cheaper/easier than flying to Florence, then maybe fly INTO Rome...but immediately train up to Florence to start your trip. That's how I did my first trip to Italy: I flew into Rome and started in Venice (train immediately to Venice upon landing in Rome), took the train south, and ended my trip in Rome and flew out of there. Sure, I could have flown directly into Venice...but I got a nice direct flight from the US to Rome. I would have had to change planes in Europe to fly into Venice. The train from Rome to Venice to me was the equivalent of a connecting flight, but I much preferred being on a train vs. worrying about missing a connecting flight on the way to Venice.

Florence is a much shorter train ride from Rome than Venice was for me. Plus, now there are even a few direct trains a day (I think) from Fiumicino airport in Rome to Florence. (but most likely, you'd need one connection in Rome to train up to Florence).

I would go straight to Florence by train as soon as you land in Rome. There are 70 some trains between Rome and Florence every day until late at night. You can take the train at the airport and change at Roma Termini or Roma Tiburtina (Rome's main stations). Twice a day there is also a direct train going to Venice (stopping in Florence along the way) starting from the airport and requiring no change at Roma Termini or Tiburtina. The total train journey is just over 2 hours (1.5 hours from Roma Termini).

You can also fly directly to Florence, but since Florence airport has only European flights, you will need to have a layover somewhere else in Europe (e.g. Frankfurt, Munich, Paris, Amsterdam, Zurich). Flying to Florence generally costs a bit more than flying to Rome, but in your case you'd save time and about $75 in train fare (full fare without discounts).

hey hey sau
when in april is this trip?
fly straight to florence. add your days to rome and plan the vatican then.
always look at your arrival times, check in to places are usually 2 to 3pm. unless you can have hotel hold luggage, where will you put is or pulling/pushing on cobblestones/unevenpavement. check out is usually 10 to 11 am.
are you flying out of naples, do you have your accomodations reserved? with people traveling all over italy with the places you want, it will probably be busy in all of them. expect crowds and lines. don't think there is off season anymore. april may have easter, spring breaks, book ahead of time.
make sure you and BF get an IDP (international driving permit) at AAA, cost $25 and two passport photos. they may ask, they may not. friends didn't have and were denied a car. it's just an FYI ( read up about it) whoever drives need one.
have a great trip and enjoy
aloha

I would not fly to Florence. Fly to Rome or Naples and work your way North.
Visit the Vatican when you are in Rome, not as an extra day. Travel by train on arrival to Orvieto, then on to Florence if you fly to Rome.
Drop Pisa and go to Sienna from Florence.