I recorded a series on how to approach building complex docs here:
There’s a post that preceded the series — it features some best practices in text form (faster to consume but nowhere near as complete):
For building systems of connected docs I suggest using Sync Tables Pro instead of Cross-doc right away. I just gently launched it last week:
P.S. Sometimes I do some sketching but usually I just follow my best practices to build docs that can adapt to changes. You can’t plan everything ahead anyway, but you can follow the system that will make it easier to make new changes as the doc evolves. My framework worked well for me and for the docs I built for clients in the past three years.