Hi Gubar

One of the first things I would say is dont try to sculpt a model that had any rigging/skinning or blend shapes on it, your pretty much asking for trouble, use the standsrd pipeling of modeling, texturing, rigging then rendering.

The main thing being is that once you import into Zbrush and sculpt it will move the original geo, pretty much no matter what.

What I do is get a base mesh thats looking like you want then import this into Z (no UV maps) then sculpt, once your happy with that export the level 1 mesh back into maya then UV and use this as a morph target to overide the Uv mesh then texture in PS (if you want to use poly painting in Z then just poly paint prior to making the morph target and uv mapping then transfer the maps to the UV space.

As for the question regarding UV maps and the multiples, if your sculpting Z dosent care if it has maps or not, although as the base level geo changes so will your maps, so your probably best off either not bothering with the UVs when sculpting or if youve already done them they will probably need a tweek, if you want you can add multiple maps to Z and render the displacements, theres a tutorial on the Zbrush wiki that goes into this.