Reservations within Italy - Milan to Venice, Venice to Rome, Rome to Pompei, Naples to Florence

Hi @thibcabe,

I have attached a screenshot from tickets.oebb.at
It doesn’t allow me to make a reservation
 

To reserve Italian trains on oebb you need to add interrail/eurail as discount and search for tickets not seat reservations.

Thank you @Al_G for the clarification.

Do you know whether the seats can be reserved at the station?

To answer your other questions;

All trains listed as Frecce… or InterCity require reservations. R and RE do not. Some routes have both types, on some the RE trains are not much slower.

They cost the same from Trenitalia ticket offices and there is no quota, as long as seats are available you can get reservations for passholders.

The only benefit of using a ticket office is that you should be able to choose specific seats.