This is the billion dollar question, but having the right answer at the outset may not be necessary. In fact, most successful business go through multiple iterations on monetisation opportunities before they strike gold.
It is more important to build a product that solves problems that Goodreads doesn't solve right now, and find a way to acquire customers that doesn't rely on Google SEO.
It is more important to build a product that solves problems that Goodreads doesn't solve right now, and find a way to acquire customers that doesn't rely on Google SEO.