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.
It does not have to be long or overly complicated. It simply has to have the elements required to put your goals into action. Developing a SWOT analysis (strengths, weaknesses, opportunities, threats) will help you to identify problems before they start. Craft your own or hire a business writer to create a dynamic plan that will guide your operations. An effective plan is one of the most important elements over overall business forecasting.