Epoxy primer

Yes, I would suggest using the epoxy over the panels you did not strip. Going over filler is fine. The epoxy will seal the old paint from the new. Some of the older paint lines will have a chemical reaction to the new paints out today and will lift/ craze the paint below even if it has been primed with a high build primer. Remember your paint will only be as good as your foundation. So if there is issues with the old paint that becomes a problem down the road. We will never paint over paint on a car. We always strip to bare metal.