ZBrush will be fine for a quick fix, high res model and as long as you stay in ZBrush, you can pose your model with little worry. The minute you try to take that high res mesh into another application...your PC just may up and die.   That is, unless your app can read displacement maps, in which case you'd only have to export the low res mesh with the displacement map from ZBrush.  Keep in mind though that you'll still need to learn the fundamentals of modeling a human and/or creature somewhere down the line. Programs like ZBrush simply make it easier for you to get the concept out but some knowledge of organic modeling will be needed for cleanup of the final mesh I think.

With that in mind, if you're looking for a pure modeler that can do displacement painting too but won't break your bank, try Silo, Blender,  or if you don't mind the stress with exporting maps - Hexagon.