[skaber]

I think the issue here is that there's a sole developer working on the whole app with the difficult choice of choosing where to start. I think that creating a design that covers most test cases of the app would then let you start from either section of the app. I am surprised OP doesn't mention anything around GraphQL (why or why not it could help).

[stepbeek]

> creating a design that covers most test cases of the app

I consider this be a very hard thing to accomplish. There are generally too many unknown unknowns. I almost always need exploratory work to figure things out.