Start with a small map and simply add attached small sections as required to achieve the ultimate size you want. That way a small area could be brought into profit then add another attached section of the same profile (flat, medium or hilly), with new undeveloped towns as now, we could then extend our empire in any direction and to a maximum size dictated probably by the capabilities of our hardware.

If you couple that with time tables then the intercity A -> B express train will arrive once every hour, or whatever time system they might implement.

Instead of micromanagement and mouse click fest I rather work with something complicated that require more thought then mouse clicks. A few trains, signals, switches, and building a time table.

If anyone who has the skills fix a mod so we can select the route for a train, and that the mod hold the train at the station until it is time to leave.