The exact experience I'm looking for is to be able to enter the ISBN for a book and download along with its usual metadata additional values like page count, illustrator, list price and Edition.
I checked out Skoob but I don't speak Portuguese.
Count Pages looks interesting but I also want to track physical books in Calibre so it doesn't really solve the problem.
But I do get the point. The built in metadata library will only support the fields that Calibre ships with. So I really need two changes. I need a way to get to the extra fields and I need a way to specify how to map those fields to fields I've created in custom columns in Calibre. So it seems like the place to start is src/calibre/ebooks/metadata/sources/amazon.py but I have to admit I don't have time right now.
Oh well... could be a fun project for the future.
Thanks for the help!