Q: What could be weather effects on epoxy/polyester (hybrid)-coated iron in a sunny and salty environment with direct sun exposure?
A: The weather effects would be quite severe. The hybrid powder will resist corrosion if formulated correctly, but the UV exposure would quickly degrade the coating. The degradation would manifest itself as chalking, yellowing, and eventual polymeric breakdown.
If a very thick coating (epoxy-polyester) were applied, this may provide protection for a longer period of time, but the coating would be incrementally eroding. Regardless of which technology you consider, it is imperative to have excellent cleaning and metal pretreatment.
As for the best system for you to consider, I recommend a high-quality polyester or polyurethane applied to a zinc phosphate or iron phosphate pretreatment. An even better system would be an epoxy primer followed by a polyester or polyurethane topcoat.