Remember the proverbial expression 'not seeing the wood for the trees'? You need to see the 'wood' first, then delve in and start examining the individual 'trees', meaning the individual items which you will be breaking down later. So a great point is to make sure that you have that overarching vision _ and if you cannot find one, then maybe it is an indication that you are obsessing on a few technical aspects that do not necessarily make up a whole business as you had imagined it. A business that makes sense and is going to be sustainable in the future is one that has that clear vision within which all the smaller parts contribute to make it successful.
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.