I’ve been doing front-end work for quite a while but I’ve always wanted to do more full stack. I’m doing a project for a friend now that’s kind of pushing those back-end skills. She’s an author with about 50 books and currently her site is on wordpress, but the plugin she used to categorize all the books is no longer maintained and is designed to work with a handful of themes that are no longer available.
Is it feasible to set it up with JSON files containing the book information?
I have very little/no wordpress experience. You could look if something exists that can be used to replace the outdated system.
I will focus my answer on building your own system
if you need to categorize books and want your friend to be able to update information and what not, I would absolutely recommend a database.
Discuss very careful with your friend what functions are needed like: managing (adding, editing, removing) books, categories and mailing list. Think about if you need searching functionality (by ISBN, title, author) or that you even need to be able to search the content of the books? Lots to think about, this are just something that come to mind
Deploying this project is also something you need to look into and take your time