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.
As a writer you know how difficult it can be to come up with article content at times. If you've ever had writer's block you know what I'm talking about. There are several things you can do to make it through the writer's block phase. One of the most popular is brainstorming with a friend or family member. Another option is to rewrite the articles and blog posts you already have written.