> requiring you to set up a "small one-person business"

At least the german tax office will take notice of such pseudo self-employments and act accordingly. Not a great idea.

What are you implying? The structure for contracting or consultancy in Ireland and most of Western Europe is exactly that - setup a one-person LLC or act as a sole-trader

https://pjf.ie/business-sole-trader-vs-limited-company/