124 cc body prep

well i've smoothed out my entire engine bay and I'm doing the exterior now , just wondering about applying body filler. i've chipped off all the bog that was previously on it (half a centimetre over the ENTIRE rear quarter panel) and made the whole panel bare metal, now when applying bog should i put some sort of rust preventative or primer. i've already bogged up the quarter panel without that stuff but just asking so that i know whether to paint it for the rest of the car

Body filler should always go on bare metal. After getting the basic shape you can then apply primer or filler primer. To finish off and deal with any remaining imperfections or incorrect shape I use 2k stopper which is much finer and can be applied over primer. Use a guide coat (light spray of black) and flat it back with a block. Any low areas will be highlighted as the guide coat will be left behind. To correct this you can either apply another coat of the stopper or keep priming and flatting until the surface is totally smooth and flat.

The amount and quality of preparation you do is what makes the quality of the finish.