I started my first business about 15 years ago and can comfortably say that while the basic process for setting up a business to handle growth hasn't changed much in that time, the tools have changed IMMENSELY. For a small investment, these tools will help you set up your business for sustainable success.
Financial projections that make sense in your business domain, and cross-foot with available data from independent market analysts are no guarantee that you can deliver. They do show you already stand out from the crowd of talk-only entrepreneurs, understand financial realities, and are willing to commit.