It’s not correct - there are different ways to qualify for a gold card. Income is only one of them, and company income isn’t too relevant to that.
It depends on sole proprietor of what? As said fapiao’s depend on how much you make a month, officially. Some places get this yellow sticker that don’t need to give receipts but make way more than the expected maximum. It all depends on your accounting, working the books. And as you said if your customers want receipts or invoices it’s better to go all the way.