give it AUV or GUV tiles for UVs in Zbrush ---> export this mesh and the maps as the hi-poly mesh (see Zbrush central for tutorials) ---> either re-topo or export your lowest poly mesh and UV the mesh using Max/Maya/XSI ect, then export---> then combine the 2 in Xnormal (free program), add low poly mesh in the low poly…
I would retopo it, I would never use dynamesh for animation. as for the polypaint you would need to UV the model, and bake the polypaint to UV space. things like this can be tedious, so best lookup tutorials.
If the model has UV's you can use the Multi-Map exporter in zbrush (under plugins) to create a texture for it. You can lower the dynamesh resolution but you'd probably be better off retopo-ing. Zbrush Central has plenty of tutorials