The project seems to require a good blend of business understanding and translating it into a technology input document. Given it is at a business plan level, it needs to sufficiently balance between being focused on the topic and at the same time being wide enough to include a wider perspective that would help the readers to be independent. I would like to propose a customer centric approach that I use for most of my business documents. It helps maintain a discipline, is focused, holistic and relates to business goals. As a business leader in my previous roles I have managed technology teams, run businesses, create plans, create cash flow sheets/ projections and am able to stitch the different elements of a good plan into a cogent readable document.