What are the essential elements of Android for a React Native developer?

I have been working with RN and I am enjoying it until now. But now I feel I should learn more about the native development of Android, I think it is necessary to develop native components and access more low level things that RN can not achieve. So I wonder about the next steps.

  1. What are the Android MUST be known to an RN developer? Should I take the Fundamentals course for Android developers or is there a better way?

  2. Can you recommend some courses / books on Android development from an RN perspective?