There's a difference between decorating cookies as a hobby, or decorating with the intent to run a profitable business. Sounds like that "general rule" might have been created by one of the bazillion bloggers fabulous at decorating but not especially business savvy. Bloggers often move on to more lucrative ideas while their initial statements become myths that will not die.
Double check your math and ask someone else to do the same. All my recipes went from a 5 qt mixer to a 30 qt, and some were even scaled up for a 60 qt. Only a couple of times I've had a problem, and it was from fuzzy math. Good luck.
Use a shortbread recipe with no eggs, no leavener, very little sugar, and enough flour to hold the dough together. Make sure your dough is chilled before rolling, Do not use warm cookie sheets. Good luck!
I'm sorry, puddles, but we understand and validate your feelings. Maybe he just needs time to get adjusted to a change. Too bad he can't be supportive right now; sometimes husbands can be real jerks. He'll get over it.