This approach tends to work better for articles that are jam packed with information and/or those that take a broad, aerial view of the topic, but it can also work with articles that are a close up view of one specific topic. For example, I've written many articles on how to create an effective resource box, and from that one very laser beamed topic I have branched off articles on extremely specific elements of that already specific topic. I assure you, no matter what your article is about, you can write about it more in depth in a new article.
Because newsletter templates are available in all variety of lengths and sizes, there is really no limit to the content that you could potentially write. Keep in mind, however, that you should probably keep down your word count to a level that people are comfortable reading. While you may think everything that you are spouting off is fascinating, it's helpful to first sit down and make an outline of what you want your main message to be, or what the major news is that you are trying to share.