Hi Lukas.
The main guideline to follow here is isolating your original content for Google News. This means having the non-syndicated content in its own directory, making sure it's the only content you're submitting in the XML sitemap for News, and when you are accepted into Google News, making sure you keep all the syndicated content out of that news subdirectory.
If you do that, it's fine to have all your other syndicated content in the /SYNDICATED directory. I wouldn't about linking to these articles from other parts of your site. Google won't penalize duplicate content that's syndicated, they just attempt to determine the original creator of the content and filter out the syndication partners from the search results. There's no harm at all having this content on your site or linking to it. As for using NOINDEX or a robots.txt disallow on the syndicated content, it's largely up to you. I know some SEOs who prefer to signal to Google to stay out of there and keep it out of the index, and some SEOs who let the content be crawled and for Google to make the call.
The most important thing is to create a clean, news-only section of the site and only submit that for Google News inclusion, and maintain a sitemap just for that section.
Good luck!
Matthew Brown
Moz