I am wanting to make selling nucs a viable little side income. I've got a 5 year plan of growing it to 50+ nucs a year.
I think that if you want to earn with nucs, you need a good reputation. 3 frames nucs are really bad to nurse to beginners. 5 frame is a good start and far much better than package bees.
When you make nucs, you should have huge hives which produce bees to the nucs. Then the nuc makes the brood and it takes only 2 weeks.
You should care about varroa too that they are cleaned quite well before selling.
Practivally 3 frame hive is to me mating nuc. It is a mere nuisance alone. When it is good flow, it fills itself with honey. I can move frames to bigger hives and give empty combs to be layed.
.One thing is too that you need quite much new combs to sell. In that job you need big hives help.