I made a basic bone setup in Maya to give him a pose. Rigging with lowpoly is better as while weighting you don't have to worry about heavy mesh and can work with it easily. Also to note, I always make animated frame so that I have basic T-pose in first frame and final pose in like 15th frame or so. This is good so as to interact with zbrush. As in, if done this way, I can export t-pose in zbrush, work on details and then re-export the final pose again to zbrush, and all the details done on t-pose will automatically transfer to posed model. This comes in very handy and you can go back and forth. I also smooth my model this time to see if all the deformations are good and if needs a change; do needed changes on lowpoly model.
1. For you final pose, always save your tpose keyframe and then another keyframe for desired pose.
Mesh detailing, Displacement and Bump maps in Zbrush:
Now comes the fun part. Beforehand I plan everything out. This is very important part of detailing. I plan how much detail is needed from displacements so that it would affect contours and how much from bump maps for fine detailing like skin wrinkles and pores. I export my posed lowpoly mesh to zbrush part by part and first start detailing displacements. Once done with displacements, I load the bump viewer material in zbrush and start painting finer details in projection mode. Note there are few settings you have to keep in mind for Maya and zbrush to impost the mesh before and while detailing.
Some things you need to keep in mind before exporting from Maya are:
1. There should be no overlapping in UV's of the mesh.
2. Try to make you model all quads. There should be NO n-gons in your model.
3. There should be no holes in your model. Though it works sometimes but try to ignore it.
4. All the uvs should be in 0-1 space of UV editor window.
Some things u need to keep in mind while importing your mesh in zbrush are:
1. Always check uvs overlapping in texture check.
2. Store your lowpoly mesh as morph target if you intend to export displacement maps.
Here are few renders I achieved using zbrush detailing and then rendering in Maya with a very basic light setup.