I'd abandoned architecture "is One Activity for all the application" and did all the usual Activity.
The problem, apparently, is to break the application functions into loosely coupled modules. Razreshite and sign your screens and functions that belong to each of them, and think about which features are independent from each other, and which are not.
Read about the SOLID principles that help to understand how best to share responsibility classes between each other: https://realm.io/news/donn-felker-solid-part-1/
Separate the business logic from the UI logic and data storage logic with architecture Clean: fernandocejas.com/2014/09/03/architecting-android-...
Organize communication UI and business logic using the MVP approach, where Model is the UseCases (they are also Interactors) of the Clean: antonioleiva.com/mvp-android
Try Moxy (https://github.com/Arello-Mobile/Moxy)
as a library to implement the MVP, it will save you from writing large amounts of boilerplate code and some of the problems with the coup of the screen.