Hi Andrew...
One of the nice things about simulating locomotives and trains is that
-- unlike aircraft scenery -- the rail lines your train will be
running on always pass the same views for scenery. Aviation scenery is
very CPU intensive, because we have to be able to view it from any
angle, at any moment.
You'll want to have a display that shows the position of the throttle,
engine brake, reverser, air brake, and so forth, along with the basic
locomotive control panel (luckily they're much simpler than an
airliner), and the external view.
Using an external control column would be ideal, and relatively simple
to accomplish. You could write the software with the option of
including the control stand in the visuals, or excluding it if someone
had a physical mockup to work with. That way, they could a) play the
simulation with keyboard or mouse and b) just get the external view
and instrument views in larger format if they wanted to run a control
stand.
The only real instrument you need is a speedometer, (with a distance
measuring gauge to tick off carlengths in more recent locomotives).
You might even be able to run the speedometer as a separate video
output and use two monitors (the other dedicated to the external
view).
Good luck with the project.
Ted