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.
Contextualise Your Budget _ Of course your budget will be extremely important. But sometimes people sort of pluck figures out of thin air, not giving it the context it needs in the business plan to make real concrete sense of how that budget is going to work. So it is crucial that every time you mention financials in your business plan, to really give them the correct context. When I have worked with clients in developing business plans, there has been a budget or amount set aside for example to be spent on marketing, which has been decided a bit arbitrarily. I mean with no real research, no understanding of what that amount needs to be spent on, and what that budget will truly achieve. It seems to have been put there to fill the need to attribute a certain sum to marketing. Make sure you are researching each point of your budget, make sure that you are giving it context and it makes proper sense within your overall plan.