With the pre prep all you have to do is mist on one coat, heat set it for about 15 seconds, mist another coat, heat set for 15 seconds then shoot which ever paint you want. Hold your air brush 6-8" away from the body when misting. It works with both wb and lacquer paints. To answer your last question if you use the pre prep the ghost farts would have been virtually eliminated. I use it when doing shadows and when layering paint colors in the same area.
Also when doing your drop shadows don't use just straight black. They look more natural with an over reduced transparent smoke or window tint. That will also allow you to build up the color and have more control of the shadow.