There was a link to a nice texture painting tutorial on the FGD wiki, but I can't find it anymore. I used only three different colors (also different hues), began with the darkest and painted the brighter ones over it with a sharp edged brush and medium opacity.
There's a big problem with the model. You forgot to apply the scale and rotation and therefore the model is huge and stands on its head in-game. It's possible to scale it in the level file, but I can't change the rotation (maybe one of the programmers can do that). Otherwise you would have to animate the adventurer again, because he gets distorted by the armature when you apply the scale and rotation. I think it's not possible to fix that. Also, the center point of the model should be on the ground. Currently he's half under the ground, because the center is near his hips. And you should name the mesh and materials in the future.
BTW, the model is not messy at all, only the face vertices had to be tweaked a little bit.
Edit: I just exported him without the armature and he looks great, although he's a bit big (2.3m (but at least not 100m anymore)).
In OD 1 Blender unit is 1m.