1. If what you produce and sell infringes his patent right, it will definitely not work. Whether your product infringes his patent right depends on his authorization text to determine whether your product is within his protection scope.
If you think his patent is suspected of plagiarism, you can go to the Patent Reexamination Board to declare his patent invalid, but you have to submit relevant evidence. The invalid patent is invalid from the beginning. After invalidation, there will be no infringement problem. However, did you infringe the patent right of the patent he was suspected of plagiarizing?
3. You sell the product for which you are applying for a patent before the filing date, which belongs to public use. Others can submit relevant materials during your application, and your application will not be authorized; If no one mentions it, even if it is authorized, others can invalidate your patent according to this article.
I hope you can understand, don't be smart.