RE: Hobby resin Vs Home depot resin
You should avoid using thin coats of resin as they will not cure properly when very thin. You need to have thick coats (25mils +) in order for the material to react and cure properly. Thin coats will stay tacky for days, weeks or months if there is not enough material to fully react and cure.
even if you have to go back and sand out the brush strokes later that is better than a coat that never cures and will soften and haze when in contact with the water.