So, I can see that you are passionate about mapping, but I would really attempt to learn Hammer properly and also learn level design theory before you attempt to do this.
You have used the default brick texture and skybox texture - the default brick floor does not work properly, because it does not fit the theme of the map. The skybox is also not good, as it does not fit the style of the map either; the Beta has plenty of skyboxes to choose from that are much better.
That floor texture inside the train-car is meant to be for a decorative ceiling. Notice how it has a cross-pattern. You should use either a wooden plank texture, or a rusted metal texture.
Using the same ceiling texture as the wall texture makes the train-car look very simple and not great. I would change it out.
The scale of the traincar is also wrong. You have not fitted the traincar to the Hammer grid size, resulting in cutoff textures. I am assuming that the floor texture size is either 128x128, or 256x256, so the floor must be a multiple of this.
It is also much too large for the NPCs in it.
There are no AI path nodes.
There are no lighting sources inside the traincar, nor are there any outside either.
I hate to be an asshole, but this map seems very unfinished. I would go and turn this map into a full creation, because this is more of a diorama or setpiece than a finished map. It needs lighting, a realistic scale, realistic textures, NPC variation, NPC path nodes, and a better skybox.
As for the gas mask citizen, you will never have the original. You must find a recreation, by gmadador or etc.
I hope this helps.