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.
So if you can put this all together, you can have a complete business operating plan that would show you exactly what your business would need to do to give you the income and profit you would like to have and a rough idea whether your market would support it or not. All you would have left to do would be to figure out how to make it all happen.