Application technique of body filler greatly reduces labor. Long smooth horizontal controlled strokes. Almost like painting or a pro drywall tech. Spotty application is a waste of t&m. I don't use Bondo. That's a Wal-Mart product. Have fun. Quality body filler is easy to apply and sand. Rage Gold is old tech. Rage Ultra is much easier.
Not sure why you did not apply filler over epoxy, get it straight and then apply primer. Standard industry practice. Wasted time and materials. I can swipe an entire quarter panel with body filler easily. But I've been doing this for decades.
Ditch that tiny pallet and use the biggest one you can. I use a piece of aluminum and clean it after each use. If you do get some residue just grind it smooth. Clean your spreaders with l thinner or w&g remover while the filler is still soft. Sounds elementary but makes doing this as a profession easier.