For texture use Multitexturing shader on the terrain to add up to 4 textures , tiled on the whole terrain (find it in the Wiki).
For creating terrains (not randomly) use Photoshop and clouds (or some other method) and manualy form the environment with the paint brush Good idea is to have a tablet...
In case you dont know how to paint terrains , darker to black is lower points , lighter to white is high points when you import a terrain height map. You can even make a terrain in Paint but that'll be very annoying , pixel by pixel.