Hi Karsten, I’ve done it both ways: using the Finder as my database and importing just the articles I need for each project; and (more recently) importing all my source documents (in my case, a few months’ worth of press releases that will be used in various stories) into a single Scriv project and writing different drafts using some of the same material. I liked the latter because I just like working in my custom made Scrivener setup more than switching back and forth between Finder and SCriv, but either way works for my purposes.
For yours, however, I might counsel keeping your sources in the Finder so that you can use more specialized PDF editing software. then again, maybe could do that editing as the material comes in, and then import the edited PDFs into Scrivener?
Please let us know what you decide and why, and enjoy Scrivener!