18 days and counting... Still slightly confused about train situation

Not exactly.
If you go ahead and pre-purchase online and manage to get a discounted ticket (Economy or SuperEconomy fare), then you are locked on that specific train that you book. Discounted tickets are non changeable and non refundable. If you pre-purchase a ticket at the Base fare (full fare), then if you can't make that train, you can change it. Base fare tickets are fully changeable and refundable. However there is no reason to pre-purchase a Base fare ticket, IMO, especially from Milan to Florence. In that route there are 2 or 3 trains per hour and the chance of running out of room is zero. At most you'll have to wait for the next train, half hour later. So it's safe to just buy (at full base fare) once you get at the station. Besides with just 18 days left, the discounted tickets are probably all gone.

Christy, you're close. Whenever you buy a Trenitalia ticket online or in person for a train that requires seat reservations, the seat reservations come with the purchase. It's automatic. The system or the agent will assign the seats. If you buy 2-3 days in advance for the high-speed train between Milan and Florence, you will pay full fare and you will be buying a ticket that will definitely lock you into a specific train departing on a specific day and at a specific time. The plane that you be on from the USA to Italy does the same thing. It works just fine to buy tickets 2-3 days in advance. Some travelers do buy in advance online to take advantage of the great fare discounts on the high-speed runs. Yes it does lock you in to a specific train, travel date and travel time. And, it comes automatically with the seat reservations. The big difference with the discounted tickets is that they are non-refundable and often non-exchangable as well. If you have a Eurail pass, you do not yet have seat reservations in Italy. You first have to pay supplemental fees to ride the high-speeds in Italy. It's usually an extra 10Euro. Pay the fee either online or in person and you will get your seat reservations.

Christy, I assume you're arriving at MXP? Here are a few additional points..... > Prior to your trip, have a look at the Trenitalia website and make a note of the departure times and other details from Milano Centrale to Florence, starting at about the time your flight is expected to arrive. > When you've collected your luggage, make your way to the airport rail station and buy a ticket for the Malpensa Express. Specify that your destination will be Milano Centrale and not Milano Cadorna, and be sure to board the correct train. You'll need to validate your ticket prior to boarding. Travel time will be about 50 minutes. > At the airport, also buy your ticket for the trip from Milano Centrale to Florence, using either a Kiosk or the ticket office. Choose a departure at least half an hour after the expected arrival time of the airport train at Milano Centrale. That will provide a bit of a "cushion" in case there are any delays, and also some time for you to locate the platform (Binario) where your next train will be departing from. The electronic board will have the information on your train, and be sure to match the train number with that specified on your ticket (since it will likely be reserved seating). The ticket will specify your Car No. (Carrozza) and your Seat No. (Posti). You'll probably find Milano Centrale to be a bit "chaotic", but that's normal. Be sure to watch your luggage while there. While you're waiting, you may be approached by people with a "hard luck story" looking for donations. Your choice on whether you give them anything. Happy travels!

Re: using the kiosks to buy tickets The kiosk may reject your credit or debit card, but it will take cash (euro) and give change up to €20. You can choose English as your language and be prompted through the process. Lines at the ticket window move pretty quickly if you prefer that option.

Also be sure to watch the departure signboards carefully: if your train goes past Florence to Rome the sign may just say "Rome" without mentioning Florence. We have friends who missed their train that way, and we barely caught on ourselves.

In addition to the electronic signboards, there are detailed paper schedules behind glass installed near the tracks and inside the station, they give arrival and departure information for each train, including the train number, and all the stops the train makes. I think arrivals are on white paper and departures are on yellow, but they are labeled. The track number might change from the one printed, but the electronic signboard will have the correct track.

"Departures" in Italian is "Partenze". The easiest way to double check the right train is to make a mental note of the train number. It will be on your ticket, on the platform display, on the departure board, on the yellow paper departure poster.
No you don't have to save money if complete flexibility is more important to you. Lower Price = Less flexibility or no flexibility Highest Price = walk up and get on or get on the next if (exceedingly unlikely, especially in March EXCEPT you are talking if my calculation is right, Easter which is one of the most busy times of the entire year on the trains) Waiting may be more risky at Easter, you will pay top price for busy trains. I'm sure you have good reasons for not wanting to commit; if it were I, I would buy ahead with a good window for possible lateness and then that's one thing less to worry about.

Thank you all for your most helpful details.. When boarding, am I understanding to look more for the train # matching what is on the ticket rather than the destination that is on the front of the train ( just in case it is going further than Florence)?

"When boarding, am I understanding to look more for the train # matching what is on the ticket rather than the destination that is on the front of the train (just in case it is going further than Florence)?" Yes. Your train will almost certainly be going to Rome or Naples, so if you look at the board or monitor for a train with a final destination of Florence (or even Firenze), you won't find it. Some kinds of boards have, in smaller letters, the major intermediate stations, but some only have the train number, departure time, and final destination. As long as the departure time and train number are correct, you're set. Like at an airport, trains are listed in order of departure time. Near the door of each car, there will be a sign (printed on older trains, electronic on newer ones) listing the major stops; Firenze is a major stop and so will definitely be listed on your train, so you can confirm. I find it handy to know when I'm arriving at my station, so that a few minutes before, I can gather my belongings and head for the exit (you'll see others doing the same). This allows you to double check that you haven't left anything behind, instead of frantically rushing to get off before the train leaves. It really isn't hard. Once you've done it one time, you'll get the hang of it.

Just to add something: don't forget to check Italo, the private competitor to Trenitalia! They offer many daily trains, and their last-minute fares are usually cheaper than those of Trenitalia.

The electronic board usually includes a running list of intermediate stops as well.

destination that is on the front of the train There is nothing on the front of the train. Look around the doors and use the displays on the platforms.

The easiest way to avoid confusion is to use train numbers. In Italy, they are very reliable.