This'll be a quick one - and I promise they won't all be boring next.js how-tos very soon.
But I got stuck building the index the other day.
It's a simple solution: you just need to pass in props to the index page. (that's really what the getStaticProps are for. It's all right there in the name, you're building a static page ... you want some props ... you have to get them.)
One cool thing - in the Saunders book, the way he talked about the revising process for a story it reminded me of the process of refactoring and extending a bit of code. more on that someday.