Export as Cordova
Then turn into APK with Intel XDK
https://www.scirra.com/tutorials/809/ho ... -crosswalk
Intel has two options for Android, Android and Android Crosswalk, you'll need to use Android Crosswalk
To add admob you'll need to add the plugin
https://www.scirra.com/manual/184/admob
It is straight forward to update APK, you just need to increase the 2 versions in the export settings.
I can't confirm the leaderboards, check the plugins while your adding admob or maybe it is ready by default...