Ho, it's hard to keep up on this thread
We got a lot of spammers on the boards, so as a counter measure, new users aren't able to edit their posts. You will be ranked "trusted" soon, wait for a specialist to do that.
I think two of the above tutorials involve stencil nodes. I could explain here how to do it, but that would take a lot of time and wouldn't be as easily understandable and complete as the tutorials. But I can still explain or answer your questions, if you are running into problems with this.
1. Texture painting means you paint your own texture in blender's 3D-view. Basically, you got a UV-map and paint on your model in 3D-view and your strokes appear on a UV-map. This is handy in some places, but I doubt you can use it on your project.
2. Weight paint is used for rigging, read animating organic models in most cases. I wouldn't count an airport or a plane as organic things that need complex movements, so I guess you don't need that, either
3. Vertex paint is a bit of a mix of the above, you paint on the model, too, but directly to vertex data. I have used this in one or two tutorials but never in my projects, I can't remember what it does exactly or why anyone would need it, sorry...
4. Sculpt mode allows you to add layers of subdivision on an object and carve details onto the models surface. This is also used heavily on organic models or uneven surfaces, but I don't think you need it on your airport. This technique is mainly used on fairly high-poly meshes or as a bake-from model for normal maps.
I'm not sure why you asked about the above techniques, they don't really fit your project. I can still provide you information about them if you want to, just let me say that I don't see how you could use them.
Now to your suggestion: I don't know how complex your airport is, but I guess it's mostly runways and stuff like that? You won't need a separate plane for that, you can unwrap your models as is. I don't think you got complex surfaces there so you should be fine with going to top view (NUM7), select all (A-Key), unwrap (U-Key) and choose "Projection from view".
AFAIK, all game engines support uv-maps and texture maps. You shouldn't have problems exporting them. Goliath is right about inkscape for the lines and gimp for the textures. But applying textures in blender is different from lining them up in Gimp or creating them.
Oh my, I'm sure I forgot about something, sorry. I'll go back to my studies now... Looking forward to your next post