For starters, good mod!

I managed to load vehicles from other mods onto the train, but having trouble with the sprites - any vehicle I manage to load that is not supported shows up in the wagon as a vanila tank.

I assume that happens because the way you wrote the"entities" file, the loaded wagon-tank is the first in the list, and it uses it as default values if it finds no suitable sprites to load a diferent vehicle.

Anyway, while exploring the "entities" and the "graphics" folder, I did notice the total sprite count for each vehicle was 128. Does the sprite count on other added vehicles need to be at 128 too? Or do I just need to adjust "direction-count" to wichever ammount of sprites it has in the graphics sprite file, and "line_lenght" and "lines_per_file" to match it?

Or are all these assumptions wrong and I'm missing something else? Maybe the witdth/length/shift/scale values? I never modded anything by the way.