The old saying you get what you pay for really applies with paint materials.
Sand to bare metal,apply dp90 don't use anything else,plastic filler,poly primer,block sand,apply 2k primer,finish sand,then seal and base or just base.This will depend on how fine you finish your work.This is the tried and true way for me the last twenty years.
Might sound like a silly thing to add here but don't forget to sand the cured epoxy before applying Body Filler... And you must always clearcoat your basecoat...That's the way.