A suggestion for allowing greater expandability.
Instead of having 0-4 and Load/Unload, allow a Load/Unload button for each position, and expand to allow more positions.

This allows players greater customisability to Load the first wagon, Unload the second etc, and have locomotives in any position.

Otherwise you may end up with so many hard coded exceptions that maintaining it will be a nightmare.

You already can set the loaders so you load the first, unload the second, and so on, click on the loaders to see the UI. I do need to figure out something for locomotives in any position though