I've already have the opportunity to see a Gnomon Workshop Training video once, with the genius Meats Meyer, where he explains the workflow between Maya and ZBrush. Even there, I noticed not every ZBrush details remains after he rendered his work in Maya. You get a great aproximation, but not the whole thing. These are details you never would be able to do directly in Maya, and still are good enough for a 3d work, at least in my opinion. The shots you have posted in this thread are simply amazing, with those amount of details. I think when you put the colors here, they will bring details up naturally. I don't remember clearly, but I found he talked something about use a medium level of details in ZBrush to make a displacement, and the highest level for bumps only, like SwankyMonkey have said. Or use various separate maps, one for hands, other for foots and so far.