In my experience this kind of documents is done by people which hardly use LaTeX. Even so it is normally done by a group of people which collaborate on it and as long not everyone is using LaTeX this doesn't work easily. I know it from my patent submissions where it is a little similar.
Even if someone would have written a good business plan with LaTeX it is a lot of work to turn it into a good, general template, which people which just finished a business plan usually don't have. I would recommend you to search for general guidelines about how a business plan should look like and then ask specific questions here if you have trouble getting one of the guidelines implemented.