A plan like this would show you how much sales your business would need to do, what your fixed and variable expenses would be, what your material cost, labor cost and profit would need to be to provide the income and profit margin you want. You can see pretty quickly if it's possible for you to get your business to that level. I don't know of any better way than to have your business give you the income and profit you want. What's neat is you can determine what you want your income to be and your profit to be over the next few years and develop a plan that can show you exactly what your business would need to do to give you that income and profit.
Having a business plan is so important to you as an online marketer. But most people, who start online businesses, especially small businesses, do not really take the initiative to make a business plan. Probably they think that it's not necessary. But for sure there is little you can achieve in life without proper planning. More so in the contemporary times when survival depends largely on one's ability to organize your physical and mental resources well. The future is actually for those who are organized. And the future of your business is dependent on your good planning.