The domain was unregistered. I owe @sharkseo a MASSIVE thank you for spotting the domain and tipping me off.

I contacted 7books.net and 7books.com along the way - I'll write a follow up post talking about that experience at some point.

Thanks for the links - I've already looked at them to check they didn't do exactly what I do but will definitely have a proper play around. There's also librarything which I'm a member of.

Books ftw!