You can do it either way. The reason for filling over the epoxy us fillers can absorb moisture so you seal off the panel so it doesn't cause rust problems later. But if you are priming with epoxy over filler then I doubt it really matters. Plenty of companies still say filler on bare metal and some now say over primer, take your pick.
I hear what your saying, as long as what I’m doing isn’t going to cause me problems done the line. Just learning as I go .
Thanks for all the input
If I give a coat on one day, then another on the second day, does it need keying between coats? I’m doing it in my garage which is damn cold at the moment so drying is slow . Sorry for all the questions