Tony,
Do not use anything under epoxy primer. Ever. Not even metal prep.
Drop the "self etching" terminology as it doesn't pertain to anything. All primers and paints are "self etching". It's only a sales term to sell that it sticks...
Typically, guys will blast, epoxy prime and let it rest. They go to work on repairs, body work, welding etc while only taking off the epoxy where they are working on it. After the work is done, new epoxy is applied to exposed steel, then body filler where needed, then a high build urethane primer for final body work, then paint.
It's just that easy... except for the hours of labour...