Train departure frequency/price

It is extremely rare for a train to be full. If it is, most likely the next one will not be. We have never encountered a full train but it is possible during Easter weekend or some other high volume day. The two discount levels of tickets most likely will be sold out if you wait till the day before. So if willing to pay full fare (Base fare) then waiting till the day before is not a problem.

The fastest long distance trains cost more the longer you wait.

Do the prices for tickets have anything to do with seat assignments or do seat assignments even exist on these trains?

The high speed trains Frecciarossa Venice to Florence for example have compulsory seat reservation.
This site is a primer you can read and answers all questions
https://www.seat61.com/Italy-trains.htm

Yanksteve, Seat assignments exist. When you buy your ticket you are assigned a seat, whether you get a cheap ticket months in advance or a full price ticket on the day. There are not different types of seats, just 2nd class (2+2) and 1st class (2+1)

Just looked up a random date on Trenialia ( http://www.trenitalia.com/tcom-en )

Venezia S. Lucia to Firenze S. M. Novella, Monday 22nd May
One departure per hour at xx:25
"Super Economy" €29.90, "Economy" €35.90, "Base" €50.

As you get nearer the date, the cheaper fares will sell out, leaving only the "base" price.. Already for some trains the "Super economy" is sold out, leaving only "Economy" at €35.90.
The €25 fare is for over 60's and under 25's, and you need a discount card.

The longer you wait to buy tickets the less likely you are to get either the super economy or economy prices. If you wait until the day of travel you'll pay the base price, which is the most you'll pay. If you buy the day before departure you "may" be able to get the economy price but all economy and super economy tickets are limited in number and tend to sell out.

There are two classes of travel, so which you choose does effect the cost of the ticket but any seat in 2nd class will cost the base price if bought at the station.

As for availability, I've never been on a train that was sold out but it can happen during holidays. If it happens just book tickets for the next available train. The routes you plan to take are very popular and there are many trains per day.

Donna

Price of ticket has nothing to do with seat choices in the same class, as far as I know.

For instance, look at tomorrow and there are only 4 or 5 trains that still have Economy tickets left, and the first train of the day appears to be sold out. Some trains (Fecciarosso) have 4 classes of service, Standard, Premium, Business, and Executive. So a couple of those Economy seats are in Premium class and go for 44.90.

I do see another CartaFreccia beside the two age related ones - can't tell the difference between those and the Super Economy

Are you a Cartafreccia card holder? If not you can forget about the Cartafreccia fare.

If you click the small grey " i " trenitalia.com displays a pop up window with more info.

OK - that's a special card - makes it simpler.