Sightseeing on train or more days at one destination?

Where are you flying from to return to Fla.?

From Paris

I’m from Florida and I’ve been to Venice in October. Yes it’s chilly but not really uncomfortable. I’d call it refreshing after our long, hot, humid summers. It’s a great time of year to visit. I would definitely visit Venice because it is unique. Also, there are direct flights from Venice to Paris. With your limited time, you should not use it up traveling place to place. I’d fly to CDG the evening before your flight and relax in a hotel at the airport.

Other than a few special trains in Switzerland, I’m unaware of any “sightseeing” trains from Florence to Paris. Taking trains on that route is not enjoyable and the scenery whizzes by so fast that there is little to enjoy.

maybe you can just do a series of 1 might stays on the train back too Paris; one in Cinque Terre one in Nice and than the last one in Paris the night before you fly back. there is not really a sight seeing train just a a series of train changes.
I would stick with more time in one destination

Trains are great for transit. They are not great for sightseeing. I would pick a destination and stay there then return to Paris later on the 21 (so you don’t risk missing your flight). Venice is a good option, or elsewhere in France (you could even fly to Paris on the 19 but spend your time in a town/city a couple hours away)

If you have a flexible schedule you could move Paris to the end of your trip (London, fly to Florence, Rome, somewhere warmer like Sorrento, fly to Paris in time to spend several days there before going home). I always try to END my trip in the city I fly home from. Otherwise you get these random transit days.

That's a long train ride from Florence/Venice to Paris. I'm not sure how much sightseeing you can see from the train. Consider maybe fly to Venice from London, train to Florence, train to Rome and then fly back to Paris putting all you Paris days together. This will put you in Venice at the beginning of October on you way to the south of Italy. I think you have enough days for 5 cities.

Venice is a fantastic city, well worth adding to your plan for three nights. As a Seattleite (not a Floridian) I've worn sundresses in Venice and other parts of northern Italy in mid-October.

Only a few hours of the 11-12 hour train ride to Paris from either Florence or Venice will have nice mountain scenery. These routes also require 2-3 changes of train.