Four rakes of six open sided cars are available. Wikipedia tells fbb that the line is double track throughout allowing four trains to be run.
And for your complete information:-
teilstrecke = "part circuit", presumably a single trip end to end.
ermäsigt = "reduced" : the notes at the foot of the on-line leaflet show that this reduction is available to holders of various Vienna annual travel cards and "Youth" cards. Nowt for the OAPs?
Annual season tickets are available also a combined train and Ferris Wheel option - it looks as if a day at the Prater Park is not cheap. Each "attraction" (?) is separate and there appears to be no "day pass" option.
But it would be good to be hauled by steam locos from 1923, even if you had to suffer Schmieröl und Kohlenfeuer um die Nase. A discomfort worth enduring?