A well-written media kit is an excellent idea. This will provide you the best tool to not only promote your book, but be able to introduce yourself as a new author of your niche. But of course it should be crafted in a way where journalists who scramble for news worthy personalities and events will be interested.
Transparency. You should outline your project, something anyone can read. In addition, you should prepare a brief but concise explanation for why the person you want to interview is important to your project, the format for the interview (e.g. telephone, email), and any rewards or compensation you are prepared to offer. You should make yourself readily available as a contact person.
The thing to understand is that people do read things you send them, and they will judge your idea on its merits and the quality of the information you provide.