Creating a book is not an investment. Even large publishers expect to make 5,000 dollars for a successful book. We recommend every author go slowly and budget for a sustainable creative life. You could spend thousands of dollars on reviews and ads and end up with bad reviews for your book. Writing is still an artform and the best thing you can do is create the best book you can. Success looks different for different people and there are many strategies for reaching readers and presenting your book to the public, but there is no formula for success. Writing is a journey.