And how do I know where to wait? I don't know for example if my car is at the front or the middle or the rear of the train?
Do I just get on at the closest door that opens and walk inside the train, or will somebody step down and show me the way?
I actually have related experience. It's not a flag stop -- which means the train would have stopped anyway, no matter what -- but a few years ago, I was boarding a sleeper on the California Zephyr at Fraser-Winter Park, and I was the only person on the manifest getting on or off.
The train stopped with the door for my sleeping car right in front of where I happened to be standing on the platform. Both the conductor and the sleeping car attendant were at the door to greet me. (And then the conductor stepped out briefly, presumably to make absolutely sure there was no one else trying to board.)