In fact i'll do really basic texturing and specular, so if you want to make great textures i'll give it to you in obj format with textures (diff,spec ,normal) in tga format.
What tool will you use to paint ? and will you paint specular also ?

The only problem is that Coat 3D seems to invert the normal map. Instead of volumes it renders holes in XnormalMap for example !

Another great thing is that 3D Coat have an option to make a seamless texture at opening, you can, paint normal , specular and color, really fast to make a floor with rocks !
For your game packs you could make floors also like in Oblivion or Follout 3 , good ones with normal maps !
Even Ogre 3D will support normal maps on terrain system , it's already working !