in my little editor I have a shader that uses 2 rgba blendmaps and 2 horizontal quad textures for tile textures (and a base colormap and an optional lightmap, and another 2 textures for shadowmapping), you can use it as a base. not really optimized, but can be extended to use 2 quad normal+specmap textures too. anyway, too many texture sampling seems to be a bit costy, I also consider a new approach to use more little terrains or terran models instead of one large terrain...