When you are writing your proposal, attention to detail is very important. You must write everything in clear and concise English. You should never use slang and only use the technical terms that you must use. The person who is reading your proposal may be a lay person and become confused if you use too many technical terms or job related slang words and phrases. Color for your graphs and charts is quite acceptable and as it eye catching can mean the difference between submitting a wining proposal and one that ended up in the "also ran" file.
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.