With that low of a hardware spec, you'll get the most bang for the buck if you go with no lighting at all, and put all the lighting in a lightmap. Here's an example. http://wiki.polycount.com/LightMap
Color map + normal map is double the texture load for characters, vs. just a color map alone with painted-in lighting. Given that the lighting on a mobile is going to be significantly less robust than a PC, and given the increased artist time for normalmapping, it may be better to paint in most of the lighting. A good…