The Downloads section is organised based on the assigned categories, and works quite differently to the Forums section (i.e., you can't make posts there, only comments and reviews on uploads). If any single category gets too big, then we can break it into more specific subcategories. But we're a long way from having to worry about that just yet.
What you see here in the forums under Scale Model Paint Masks is merely a set of automated notification posts - every time a new file is uploaded to the Downloads section, a corresponding notification is automatically posted to the forums. So you can track what's new using the forums, but for searching or browsing the catalogue of available files, you'd use the Downloads section.
Kev