I have read quite a few articles which go into modelling game ready characters but all seem to have different approaches and I haven’t really come across one yet that describes the process simply.
Articles from The Rookies found here. This article went into some detail on game character creation, I am still a little confused as to how low poly you have to make the model after the high res has been sculpted.
I do know that you need to have a low poly version of your character modelled out that you use to bake the high resolution normal and displacement maps to. These videos gave a main overview of how to save maps out from Zbrush, simple enough but I’m sure getting them to bake onto the actual low poly model will be a problem on it’s own.
References
rendering with zbrush and photoshop – http://www.zbrushcentral.com/showthread.php?74301-Re-Angel
https://80.lv/articles/tips-on-character-creation-in-zbrush/