Disclaimer: I am not a super-expert on databases, but I am able to do database design (read below, please).
Proposal: This is the most important thing before writing a line of code. It is a must to understand the business logic in order to design the database. So I think this job to be properly done you will need to deeply specify the requirements in a document. Based on that document I could design the database for you and decide the correct relationships between tables. I think I could do this job in 1-2 days after getting the requirements document.
Experience: 3+ years working for a startup as Django Backend Developer (I recently quit to start full-time freelancing). Our database had almost 100 tables in MySQL, working properly, and some of them created by me.