20 wagons is nothing for a train. Trains can pull much more than that. Adding a second or a third train will increase how fast the train can accelerate, meaning the cargo will be delivered faster.
The only thing I think the game doesn’t have realistic is the fact that doesn’t matter how many wagons you put, it will always run. Very very slowly but it will run. The minimum speed is 1 Km/h. I test it.
But you can definitely realistic have very long train and more than one train if you want extra acceleration speed. Extra trains is mostly necessary for slope tracks, perhaps increasing tractive effort. As I prefer to play in flat lands I didn’t test this. But keep in mind that this is very costly. I would require a lot of full wagons to compensate the cost.
