One of the first things to consider is what kind of data you have to work with in your cash flow template Excel spreadsheet. Ideally, you're looking for accurate monthly data including income statement items like revenue and operating expenses and balance sheet items like equipment purchases and cash from financing activities. If you have a longer time frame you can go with quarterly periods, but annual tends to be too long. After all, how can you predict what is going to happen beyond 5 years with any accuracy unless you're valuing an annuity?
Business expenses come even before you earn your first dollar. This is the first business consideration you have to thoroughly think about before you begin promoting your business, the expenses necessary to operate your business.