I"m not sure if characters based on the books are "no problem", understand the books are copyrighted too. It's not true that "as long as you don't make money it's not a problem". If it is found you infringed on a copyright you are guilty whether you give away the items or sell them. It may be "your vision", but it is "their copyrighted characters". In some cases "they" may not notice your product, but if they do, you can be sued, and the cost to you can run from ten's of thousands of dollars to millions.