I think you should add wheels to your train, add vents on the top of the train, add some NPCs ,Add a front where the engineer and operator work. Add some colors because it looks boring and add a back door with a metal deck
I really like the exterior of the train it looks really nice. The only problem with it I see are that the seats are too simple. I think you should give the passengers some armrests and put some space between the seats so they arent sitting on top of each other.
You’re doing good so far. Might I suggest adding textures to the interior of the train and adjusting the lighting as well to add detail. Blender is also something you should look into, it can help a lot to make your creations look more detailed and realistic.