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.
If you work in a Human Resources/Personnel department at a large corporation, or work for a small agency that sells temporary labor or executive search services, then you're in the business of evaluating personnel needs and pitching people and their skills. You may need to convince your boss or a new client of the need to create one or more new job positions, or persuade the boss or client to fill existing positions with personnel you recommend. Perhaps you are persuasive enough to do that with a phone call or casual conversation in the hallway, but odds are better that you will need to write a proposal to pitch your ideas and persuade the client or upper management.