You can freeze the cake, depending on how much ahead of time you want to make them. I wouldn't freeze them after dipping, because that will cause the coating to crack and thawing will give you condensation issues. Since dipping seals them, they'll be good for at least a week afterwards.
As far as pricing, no one can tell you how much to charge. It depends on your location, skill level, cost of ingredients, overhead, how much you pay yourself, etc. I charge $2.00 each for the most basic of mine, $2.50 to $4.00 for really decorated ones.
As far as making a dozen at a time - not worth it. Unless I'm doing at least 3 dozen, I don't bother since they're a pain. But folks seem to be really impressed with them. Go figure . . . .