I've discovered a problem! In order to center a 5tile car on a 20x25 lot, the car has to center on 25 tile width, leaving the shorter 20 tiles as the length. Placing the 5tiles in the center of the 20, means the train car doesn't actually center. It's one tile one way or the other.
A 4 tile wide car with only one space of hallway or a 6-tile car with exaggerated spacing center on the 20 tiles and allow reversibility of train cars.
A 25x25 lot would allow the 5tile car to center and be reversed.
Just trying to put this out there before it's too late and sorry I didn't think of this earlier.
Added: My vote now would be to keep the 20x25 lots, but just bump up to the 6tile train. It's looking nice on the converted trains from the Elf Express lots. This is the size I get from extended the Elf Express Caboose House. I think it's now basically back to option C, but it's 22 long:
https://cianesimshome.files.wordpress.com/2020/01/screenshot-24-2-e1578089755491.jpg
https://cianesimshome.files.wordpress.com/2020/01/screenshot-26-2.jpg
I'm obviously still playing around it, but wanted to post size and line up of wheels and windows and doors and stairs. I didn't think the pedestals were needed (behind the wheels), so these pics show the wheels without them. I'm still open to the 5tile version, but I do prefer the nice symmetry of going with the 4 or 6 tile and being able to reverse the cars.