From my point, research interest is what you want to do. This is required by applying to faculty position. If you just want to be a postdoctor, you only need to prepare cover letter, CV and three recommdation. The cover letter should be brief and detailed what you have done before. You can attach the your dissertation abstract not your whole dissertation and your published papers (whole paper) if you have.

If you want to metion about what you want to do in future, please only use one or two sentence to explain them. And these interest is better associated with lab's research which you apply.