Use multiple loop templates for displaying content only from certain categories. For example, images fall under the Gallery category, with all relevant subdivision being done with nested subcategories of that main category. So:
Gallery > Fanart > Post [Somehow associate with user account]
Fanfics > Genre > Post [ditto on above bracket]
– Use custom post types or formats to control how each page displays?
– Is there a limit on how deep category nesting can go?