No to dampen your spirits but I wouldn't go there. Don't design your own gearboxes. We can tell you what you need to know but even the top teams buy in parts like gearboxes unless they have very high end manufacturing facilities.
If you really want to do it I suggest buying a few old gearboxes for feathers like Banebots or Gimsons and seeing how they are assembled and built but you will waste a lot of time and money by going down this route and it will give you no advantage at all. Sorry, but its true.