1.)
I think creating a terrain is not that great problem.. (you said that you created one with 3dsmax)
2. - 4.)
you just set the blendmap on your modelskin 1 (in MED)
The blendmap is:
Black = 2nd Modelskin
Red color = 3rd modelskin
Green Color = 4th modelskin
Skin 5 and 6 of the model are for players with PCs of non-shader compatible hardware.
All you need to do is draw a Black/Green/Red Picture and set this as Skin1
On Skin 2-4 you set different Textures.. f.e.:
Skin2 = Grass
Skin3 = Sand
Skin4 = Rock
5.) just use
entityname.material = mtl_terraintex3;
the difference between mtl_terraintex3 and mtl_terraintex is:
http://www.conitec.net/beta/amaterial2.htm#mtl_terraintex