Writing a book even a good one does not guarantee it will sell. Knowing how to sell and promote the book, launch it and use all the right tools in the right way is a different expertise.
Have a marketing agency with the specific working framework for self-published authors.
Many subjects have vast amounts of books written about them. If you really want to get the picture you’ll need to read a lot of them.
Read all the relevant books, and summarize them in a single book. This book will give the readers all the main important information they need at a fraction of the expense of time and money.