On first glance, I would use a 1024 without tiling to create a starting layer of simple, general diffuse colors. Create a second UV channel that uses some careful tiling and / or mirroring to overlay grime, stains and discoloration on top of the basic coloration. Layer that onto the diffuse in the shader. If you're using…
All right, had time today to get this thing going. The vertex paint is the way I'm going to do it. As you can see by the screenshot (definitely not final textures, just a TEST!!!), works fairly well with diffuse textures, so it should work fine with normals as well. I'll be using a 256 x 512 tiled texture for the main body…