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.
Wedding cards should match and have the same design of your wedding theme. The modern and sophisticated way to write the wedding invites is to use a love poem, wedding verse or write something that will match the wedding theme.