Yeah I think all you need to know about the "gray area" is the threshold of "tax evasion" or "tax fraud" in your country, and don't get even close to it, for me I'd still be worried to make a mistake and it would be on the back of my mind, so as you are saying, if you want to make things right and easy, incorporate a mini-GmbH, use professional help, and focus on your product.
