Using an outer 3d program to combine meshes will be better. You can simply decrease the vertex count as much as you can within.
Also about Fog question, from what I see on the forums, people use a way to change the color of everything depending on the distance of the mesh. For example everything at distance 10.000 is pure black no matter what, and they are lerped to their normal colors as they get closer.
Asking about it as a seperate question might help you on that part, as I have little to no exp on such a thing, but it is possible? Yes.
=)