There is a decision here that you can decide to render every single event kind as a notification (seems like a lot of work) OR broadcast the received event to the phone. Nostr apps would keep listening to the broadcast and render the notification themselves with this: 
https://developer.android.com/develop/background-work/background-tasks/broadcasts 

 Yes, I was thinking on this part. My approach will probably be both. I just wanted to make sure the isolated notification system works. Iḿ going to clean up the notifications for kind 1, connect to Amber, and after that investigate the boradcasting