What engine/renderer are you using? You can either use a Vertex Blended shader to 'paint' the cracks on your mesh, or you can use decals. Not sure which would work for you best. Also, basing this off any artwork? Cheers!
Sorry, was on a lite device, so missed half of the stuff in the OP. Here is the link about vertex painting: http://www.chrisalbeluhn.com/UDK_Advanced_Vertex_Painting.html Looking at your concept, I would say you're in a good place, although I suggest before you go any further to try and improve what you have currently.…
@Ace-Angel: He linked the art work in the post right about his screens, real easy to miss. Heres something I've noticed recently while working on my new scene, doing a vertex blend of two or more textures is cleaner in your editor/view port, but I don't think you get the best result, at least not with something like cracks…