1 START with DECIMATION

You need to decimate as much of your individual parts as you can. This will accelerate the baking process time and you will have a usable high-res mesh if you need to retopolgise. For decimation, a good rule of thumb is try to aim for 300-350k polygons in Zbrush. If too much of your detail gets washed out during the first pass of decimation try a higher count, or if nothing changes try a lower polygon count. The goal is to get the best result with the fewest decimated polygons.