1, you definitely need to register a company, and you have the same plan.
2.DM is not a magazine publication and does not profit from sales, so serial number is not needed. If it is a magazine, it is difficult to apply for a serial number, and it needs the approval of the State Press and Publication Administration. As a DM, you only need to have the advertisement number of the industrial and commercial administration department.
In fact, many people are doing this now. If there is no specific advertiser support and you are not as optimistic as you think, I have operated this thing. Your distribution network and distribution volume must have certain data and scientific detection methods to convince your customers.
4. In fact, the state departments don't have too many requirements in this respect. Cultural inspectors are willing to crack down on piracy. They are not interested in this and do not pay attention to sales profits.
I hope you can succeed!