Venice to Ferrara to Ravenna trains - are trains full (of people) :-)

Regional trains don't "sell out", but they could be standing room only. But if you just show up 20 minutes before departure, when they spot the train on the platform, you will be the first on board to grab seats. The regionale veloce trains originate at Venice S Lucia and they are not much slower than the "fast" Freccia trains.

The Frecciarossa trains are headed to Rome, and require seat assignments, and it's more important for those long-haul travelers to book ahead and save money. The Regional trains running to Bologna end there, so they won't be "bulked up" with people heading elsewhere. April 25 is the Liberation Day holiday which may be another reason for people to book ahead to travel to Rome.

Second class tickets can sell out on reserved trains, and likely you'd have trouble to seat multiple people together on short notice; first class is less likely to sell out. Regional trains cannot sell out and I doubt that you'd have trouble to find seats somewhere, especially when starting from the first station of the train (e.g., at Venezia S. Lucia, vs. more Italians may board at Venezia Mestre). I happened to take a train from Ferrara to Venice this fall but don't remember anything special about it.

The discount tickets are now sold out (for Friday April 24)

No they are not. All Italotreno's discounted tickets are sold out (because the 25th is a national holiday), but there are discounted tickets left for Trenitalia's high speed trains departing to Ferrara at 6:53, 9:26, 10:26, 11:26 and 14:52.

Thank you.
I bought our tickets a few days ago. It is my first time doing them online.

One lesson:
I tried to register at Trenitalia (sp) and failed
So I just went ahead and purchased the first set of tickets. On the last screen I was asked if I wanted to create an account. So I tried again an succeeded. However, the purchase I had just done doesn't show up in the account.
I stayed logged in and purchased two more trips.

I tried to register at Trenitalia (sp) and failed

I managed to register last year - it was really handy. I could buy tickets on the fly with the Trenitalia app without needing to re-enter my name etc. each time while I traveled around Italy - just a few taps on my phone to buy tickets. Really easy.

The trick for Americans is that you need an Italian tax ID - a Codice Fiscale. You can just generate one using the instructions on this article below.

http://www.italychronicles.com/how-to-create-a-codice-fiscale/

Why register? It seems a waste of time, unlike Italotreno Trenitalia offers no discount codes for registered users.

Just note down the pnr code of your tickets, or keep the purchase page open till you receive the email/text with the pnr .

Not all Regionali trains are full of people, and when they are it’s usually at commute time, as those trains are primarily used by commuters traveling to and from the main cities from the suburbs.

In any case look at the silver lining. Even at commute time Italian trains will never be this full.

Why register? It seems a waste of time, unlike Italotreno Trenitalia offers no discount codes for registered users

Not a waste of time at all, at least for me. Registering saved me an enormous amount of time on my last trip to Italy, because buying even regional tickets on my phone requires entering my name each time. When I register, I can skip all of that and just buy a ticket with a few taps of my phone. I have my Paypal account already included, so I don't have to enter payment info each time.

Sure, I could just buy tickets without my phone from a machine, but then I have to wait in line sometimes. I bought most of my tickets on my last Italy trip at the last minute - that is, I would day trip to a town and maybe 30 minutes before I was ready to leave, I'd buy tickets on the next train back. Very easy. I know not everyone travels this way. If I were taking the fast trains from Venice to Florence to Rome and buying them far in advance, registering might not benefit me much.

Yes, Andrew but on android phones it's the browser that stores those data and automatically fills the relevant modules with name, surname and email. It's something users don't need to take care of, while getting a codice fiscale requires to make a bit of research and to use sites not translated in English.

Same for the app, you must install it bypassing the regional block on the app store; on the other hand the mobile version of trenitalia.com works quite well and it's already in your phone, ready to be used "on the fly" without having to wait in line in front of the ticket machines.

I guess it's a matter of "tech tastes", I like to install only the apps I really need on my old mobile phone.