Do not try to write your business plan in one sitting. As I mentioned in the beginning, for a traditional brick and mortar business, it could take in excess of 100 hours to compile all of the information needed into a comprehensive but yet understandable document. For online businesses, probably not that long. But your final product should be well thought out, well documented and easily understandable.
Executive Summary _ A business plan starts with an executive summary, which is a one or two page summary of your business plan, or an introduction to your business. Although this section is at the beginning of the business plan, it is the last thing to be written. You'll be able to condense your business plan more succinctly once you have the opportunity to work through the other parts of the plan. The executive summary may be the only thing a potential investor or financier will read, so write it last because it has to be the most compelling.
I suggest that you construct easy to read tables and graphs for the financial portion of the plan. The worksheets suggested are: Salaries/Wages and Benefits, Outside Services, Insurance, Advertising Budget, Occupancy Expense, Sales Forecasts, Cost of Projected Product Units, Fixed Assets, Growth (or Start_Up) Expenses, and Miscellaneous Expenses. You may find some of the worksheet templates at PlanWare.org to be useful.
So, although a detailed business plan may not be required for an online business, I am going to include it here so you can at least look at and consider each section and determine yourself if it applies to your business.