Appendix - Resumes of principals/management; letters of recommendation from current business associates/customers/suppliers; marketing research data; demographic data; leases or contracts in place or as promised; business licenses; price lists from suppliers; trade or industry articles or data; floor plans; information on subcontractors; liability insurance policies.
One key component critical to your success is scoping the competition. A business plan consultant studies the area where you will be located quite thoroughly. For example, if you plan on setting up a coffee shop on Main Street, or within the vicinity, the small business consultants you consult with will inquire about the number of existing coffee shops and the services they provide.
U.S. Census Bureau (census.gov): A source for a variety of useful statistics, especially the Economic Census that comes out every 5 years.
You may find that the easiest part is the actual writing of the plan. The real work comes in the data-gathering, which may take you a hundred hours or more, depending on what you already know or have researched. If your new venture is in an area where you've been working, you may already know about your customers, your suppliers, your marketing plan, your organizational structure, your financial and cash flow needs, equipment, inventory, and so on.