I'm always amazed, too. It's incredible to see those rides are build up within some days. 
I can only speculate about the train size. At the Oktoberfest in Munich they run every train with 7 cars...maybe it depends on the size of the fair 
( about 6 million visitors every year in Munich and about 1 million in Düren ). 
  
For it's age - Olympia runs very smooth