Making your own app

I've got 2 questions about making an app.

Is the procedure (between "I finished programming" and "I want to use it") for making an app that is only for yourself different from making an app that you want to make available for everyone?  Meaning if I make an app just for myself and I notice a mistake in my app I want to be able to correct it and use it immediately.

Is there somewhere a list with all the variables and commands that are specific for making an app for your Garmin?  https://developer.garmin.com/connect-iq/api-docs/ provides already a list, but I'm missing some things.  For example I'm not seeing the word "distance" in the index.  Is there a variable that indicates the heartrate limit that's being used?  Is there a command that makes the alarm sound (with or without the vibration)? Or maybe I'm not smart enough or don't know enough about programming.