At this point, you may be tempted to skip writing a business plan altogether, viewing it as an unnecessary exercise in jumping_through_the_hoops, suggested by some old business professor who probably never held down a "real" job anyway. Maybe it's okay as an assignment for an MBA class, but it would be just too confining and irrelevant for today's fast_paced business environment. Anyway, you're ready! You've thought about this business venture for a long time and talked it over with friends and everybody agrees it's a great idea. Best to strike while the iron is hot!
Another consideration. Should the business plan be a document that is focused on selling an idea for a product or service? For many years I worked in a company that did not want anything in a business plan that could be construed as showing a bias towards or against a project. The mantra was to only present facts in the business plan. The Operations Research Department was there to review the analysis as being unbiased. To handle the "what if" scenarios or sensitivity analysis we prepared a supplemental analysis documents which were mostly financial oriented. Personally, I like a factual approach and use the presentation of the final document to point out the conservative aspects of the content.