Create initial extension with boilerplate code, extension configuration, test cases, documentation etc. This is a preparation for starting actual work on the project.
As for code, this should include the data classes to be used (they will most probably change over time), database tables and service classes to access the data classes. Basically an ORM backend.
It should probably also include examples of JSON data transfer objects from different root views, e.g. how a complete object graph representing recording is represented, how a complete user is represented, how a complete manuscript is represented, and so on.