Creating a business plan is a good idea for anyone starting a business. Oftentimes people think they don't need one if they are not going to be looking for money from outside investors. But writing a business plan is a good exercise for every new business owner to go through. The process of creating a business plan will bring up issues you may not have thought of and crunching numbers will be a reality check on otherwise possibly vague or overly optimistic projections. You'll also be doing it when you still have time to make changes if it turns out the numbers don't add up to making a profit.
Your business plan doesn't have to be complicated or complex; it just needs to describe certain basics about your business and include some financial projections and calculations.