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!
Rallying point: Your marketing plan gives your troops something to rally behind. You want them to feel confident that the captain of the vessel has the charts in order, knows how to run the ship, and has a port of destination in mind. Companies often undervalue the impact of a "marketing plan" on their own people, who want to feel part of a team engaged in an exciting and complicated joint endeavor. If you want your employees to feel committed to your company, it's important to share with them your vision of where the company is headed in the years to come. People don't always understand financial projections, but they can get excited about a well-written and well-thought-out marketing plan. You should consider releasing your marketing plan--perhaps in an abridged version--companywide. Do it with some fanfare and generate some excitement for the adventures to come. Your workers will appreciate being involved.