How to structure Vuex Modules for Relationships, Speed and Flexibility

Greg Bate wrote a nice tutorial on how to structure Vuex Modules for Relationships, Speed and Flexibility.

You can use Vuex modules in many ways, primarily representing single or multiple records. When using the latter it can add a lot of complexity, I wanted a solution that fit the following requirements:

Easy lookup by ID

Relatable to other records (only when required)

Responsive to changes

Fast