I agree with the sibling comment that "How to decide what you need on your devboard" is the tutorial that would be nice to see. This article is trying to do too many things at once (design a dev board, baby's first schematic, baby's first PCB, baby's first JLCPCB order,...) and that's really the only one that's novel. The rest of it is standard EE stuff that's covered in a lot of places (with varying degrees of success).

As for decoupling, I've written about how to do it in various places scattered across the internet. I should really collect it all in one place one of these days.