The expected revenues and expenses for at least a year should be projected in the cash flow section of the Financial Plan. It's better to make conservative predictions rather than be too optimistic when it comes to cash flows. As part of this section, a break_even analysis is essential. This is the "amount of units sold or sales dollars necessary to recover all expenses associated with generating these sales." (NxLevel for Entrepreneurs, 2005) The formula for calculating the break_even quantity is Total Fixed Costs/(Price _ Average Variable Costs).
You may not have thought much about your competition or outsourcing some of your work, but things like that will impact your ability to make a profit. And you will find this especially so in the beginning phases of your business. Even you are just opening a lemonade stand in the front yard, you will still need to know what Susie is selling her lemonade for on the next street over!
Start by writing a description of your business, including what stage of development it is currently in (conception, start_up, first year, mature, exit) and your plans for growth. Discuss the nature of your business, the main products and services you offer, the market for your products and services, and how and by whom the business is operated.
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.