Looking good. I think it needs a specular map. Also everything looks a bit too clean and pristine, not like a battle-hardened war beast. Otherwise looking great.
I really wouldnt worry about the low poly geometry yet, assuming you're going to take this into Zbrush I'd get a base laid down and sculpt it up before worrying about the topology too much. Ideally I'd say make it entirely in zb, but that depends on how comfortable you are with zbrush. Personally I'd push the native…