An even better model would be to allow anyone to read, but limit only registered users to be able to comment or rate. Allowing any visitor to browse and read pages.
Although ultimately to get initial traction / users perhaps remove the need to login at all unless you are submitting your work.
You speak of monetization and I would imagine the obvious routes would be through affiliate schemes with the eventual book publishers or 'premium' services for book publishers that want their book to get 'tested' by the most people / essentially top of the list.
With both of those options there is no requirement for a typical 'visitor' who is reading / ranking books to have to register or login at all.