I discard the idea of manufacturing the product. It's too much work, too little margin and I don't have time for it. I prefer to program as a web developer than to cut cardboard and manage mailings.
After almost two months, and little time available for this ...
I have modified the landing, added affiliate links to amazon, created an instruction pdf and set up a paddle so people can pay for that pdf.
The project is now 100% digital. I am selling the instructions, not the finished product.