The dots are simply markings, each species has a specific number of dots, anything from 0-24 depending on the species.
They don't mean anything except "don't eat me, I taste nasty"
Nope. They are spotted because when leaves get spotted that means they are rotting, so the ladybugs have spots to indicate that they don't taste well. The spots are randomly placed.
You "heard" granny-tale BS!