So if I understood correctly, you’re make a site for a client, and already have a list of “books” you want to import.
My suggestions :
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Create a custom post type for your books
I think it’s the best approach, and it allows you to add any custom fields you want as meta fields.
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Look up wp_insert_post
It allows you to programmatically insert posts, so you can loop your current data and for each book, insert a new post in you books CPT.
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Look up add_post_meta / update_post_meta
Allows you to set your CPT’s custom meta fields with w/e info you need attached to a book
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Curl may also be helpful if you have to grab external files.