Short answer: choose an epoxy sold for tumblers or coatings with a long enough working time (often 30–45 min) and good leveling without dripping on a cup turner. Measure accurately and plan about 1.5 fl oz per coat on a 20 oz skinny (details).
Working time: longer gives time to spread and torch on a turning cup.
Sag/drip resistance: tumbler epoxies are formulated to stay put while spinning.
Cure on the turner: plan to keep it spinning for the time on your label (often several hours).
Ratio: mostly 1:1 by volume; use a scale for small batches.
Finish: most are not dishwasher-safe; check the maker's claims and tell buyers to hand-wash.