You can't do a marketing plan without getting many people involved. No matter what your size, get feedback from all parts of your company: finance, manufacturing, personnel, supply and so on--in addition to marketing itself. This is especially important because it will take all aspects of your company to make your marketing plan work. Your key people can provide realistic input on what's achievable and how your goals can be reached, and they can share any insights they have on any potential, as-yet-unrealized marketing opportunities, adding another dimension to your plan. If you're essentially a one-person management operation, you'll have to wear all your hats at one time--but at least the meetings will be short!
What's the relationship between your marketing plan and your business plan or vision statement? Your business plan spells out what your business is about--what you do and don't do, and what your ultimate goals are. It encompasses more than marketing; it can include discussions of locations, staffing, financing, strategic alliances and so on. It includes "the vision thing," the resounding words that spell out the glorious purpose of your company in stirring language. Your business plan is the U.S. Constitution of your business: If you want to do something that's outside the business plan, you need to either change your mind or change the plan. Your company's business plan provides the environment in which your marketing plan must flourish. The two documents must be consistent.