3 - Earn first revenues
At this stage, your app's user base should be bigger but not enough to generate significant revenue with in-app ads.
We advise you to slowly move towards monetization.
This way, your app will keep driving new downloads and installs while it will generate revenues.
Configuration exemples:

2 Adstronomic SDK Ads Placements : 1 App-Monetization SDK Ads Placement

1 Adstronomic SDK Ads Placement : 2 App-Monetization SDK Ads Placements