Hello!
I started to do a game, or more precisely - simulator of the Chernobyl nuclear power station - I want to make it 1:1 with the original - I have drawings:
My goal is man to walk inside and achieve complete accuracy and maximum realism. The building is huge.
Until now I have not worked with BGE or other GE, I’ve only modeled a few things.
Is there anything I should know before I started to model the walls? Any tips?
The idea is First Person Look, but I have a problem with character:
When touch the wall, enter it, and then when button released - bounces. This should not happen, what can I do?
If you are going to make this a game engine simulation(walk around) you dhould pst this in the game engine section, or at least ask questions about the game engine there, cuz you will get more responces there about that. This section is for modeling and texturing and lighting wips so critiques go toward that.
So I guess if you are doing both post in both.
BTW, I encountered the same problem in BGE, one way to solve it is python…
As for the walls I believe there is a new Blender 2.5 feature( i see you are using 2.4x, i prefer that too btw) that makes them automatically from planes. meaning if your walls are made 2d, you can apply a modifier to give them thickness(cant remember what it is called)
Yes it is wrong section, please some moderator move it to GE
I found Phyton script for movement - http://www.tutorialsforblender3d.com/GameDoc/Movement/Movement_Servo_1.html
How to do, background image from top ortho be one image, while right orho - other image, for each are retained size offset and blend different as I set them?
The only way I think it is possible, is to split your window into different view-ports and put a background image for each.
It’s rather easy in 2.5, you can change it at the axis thingie at the background panel. Dunno about 2.4x, I’m already in the process of forgetting all the 2.4x stuff 
When you’ve done that in 2.5 you can change offset and size without affecting other background images.
You can always model the model in 2.5, as long as you don’t use any fancy 2.5 features it should be backward compatible, but I’m not really 100% sure of that.
You might want to look in dividing the building into smaller sections, with loading stuff in between, as the game engine can’t handle infinite amounts of polies. Staying as low poly as possible will help you in the long way anyway 
it’s easier to add polies than to remove em in my humble experience.
How to apply this texture to all materials faces?
Be something like basis, and on it are other textures. The aim is - where no true texture to be seen that.
In blender 2.49
Select your Object, go in Edit Mode, Select Everything, Press U -->Unwrap, Press U -->Reset, Then in the UV Editor Choose that image, Or better yet, Click Image–>New, and in the popup, Press the UV Test Grid Button.
Is there a way to not depend on the size of faces, to no difference and no apparent edges?
I guess you can just do unwrap? without the reset i mean
Without reset: 
Lol I dunno mate, but why do you really care since it is a test grid anyway?
Perfectionism 
It is good to know such a method for applying textures in which the texture is repeated automatically, not resize, becouse I will use Texture Face Materials for the game.
The map is huge and I have textures for only one room. The game will be released so… Periodically when I get more textures, I update it - purple grid help me to do that.
By the way, do you know a better method of making shadows on the texture than Photoshop?
Baking but i have no idea how it works/how do do it
Best way to make shadows is to bake an ambient occlusion map and use that as a base for your diffuse map.
Can you explain what you mean plz?
I noticed that the subject makes a shadow on itself only with Spot Lamp. My map is one mesh, but if I use only Spot Lamps, ceiling are not visible. What should I do?
I don’t know if I’m fully correct with this, as I haven’t done this myself, it’s just what I remember from reading about it:
Baking an ambient occlusion map is done within the baking tools (in 2.4x under the render panel). It’s basically a sort of shadow map. Depending on the lights you have placed in the scene it renders a map, which can be used as a base on which you paint your diffuse map (the fancy colours) in gimp for example. If you don’t add any lights it renders a basic ambient occlusion map based on general lightning.
Here is a basic tutorial (found with google, haven’t read it myself but it seems to explain the basic idea of ambient occlusion baking) http://www.katsbits.com/tutorials/blender/baking-ambient-occlusion-maps-for-terrain.php
Why does this happen?
And that wall at the end in reality will be completely dark 