i come from an automotive repair background(collision repair specifically) and if you clear use fine grit paper and if you clear use high solids clear
and always use 2 component clears. never use lacquer ! and always as said before to use the same family of resins, dont mix them in layers or become "at home chemist" and make some junk. there are billions of dollars/pounds invested in the expoxy and polyester resin industry to make the products the best they can. take advantage of all those university degrees and use the resins as they are intended.
as for prep to clearcoat--you only need to sand barely enuff to take the gloss off the part. clear will bite to the fine scratches , as it is made for that in the automotive repair industry.
if you dont have spray equipment--consider experimenting with a small roller and using high solids clear, roll it on. let teh coats almost dry between coats and mix with the 2nd component as usual and when all is cured you can wet sand and polish it to the shine and gloss you desire.
high solids clear--think of it this way, in paint the pigments are high solids, for density and color match and more efficient use of all the materials and health reasons too. for high solids clear the clear solids(pigments) are clear but have high UV resistance.
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