It is shown both on Minuetto and E464 by the SCMT plugin. As soon as you enter the field "Loco Mass" or "Train length", it should appear in the upper corner. At the end the scmt plugin is using the TSC function GetConsistLength and Get ConsistMass to show up the values. Using the default RSC will not require any data input
For the speed, you're right. You've to set the speed. Usually Minuetto is 160 km/h but it could be that the value entered depends also on the railway you're driving. (For this Mr. Codadilupo is more than expert).
Additionally you've to setup the number of drivers under the PdC field. Normally Minuetto has one driver only, but if you put 1, the SCMT system will reduce (for a specific italian procedure) the maximum speed, to something around 100 kph (I do not recall in this moment).
This is the reason why a lot of italian simmers use 2 as the number of "drivers".
Just a short hint in regards to the list of data to be introduced for the Minuetto (if experts find some of the hints wrong, pls correct):
Uso Locomotiva (Loco use) "In Testa" for the Minuetto
PMF (Braking mass perc) Depends on the route, but between 130 and 145 should be ok
Lunghezza reale (Real Length) It is suggested in the upper corner. It should be around 50 for a single Minuetto
Freno (Brake) "P" for the Minuetto. "G" is used for freight
Tipo treno (train type) "V" for the Minuetto. "M" is for freight
Vmax treno (max speed train) Minuetto is 160km/h. I'm not 100% sure that the max speed to be setup here depends also on the route condition. It should depends logically.
Rango (rank) "C" for the Minuetto (there was an error in one of my movie). This means that the speed board limit to be looked to when driving is always the lower one.
Rallentamento (Slowing down) "Treno" for the Minuetto "Loco" is for passenger train and other types
PdC (number of "man in cab") already explained
Massa (mass) It is suggested in the upper corner. It should be around 90 for a single Minuetto
Orario (time) Time of the day
Hope it helps