Just make sure you don't try going too meta too soon, otherwise you may lose touch with reality.

1) The "hello world" app you made -- did you have anyone review your code? Maybe it contains obvious errors you didn't notice. Maybe learning about them could be very beneficial in long term. Having an improvement shown in a program you already spent a lot of time thinking about could be better (more motivating, easier to remember) than reading about a similar technique in a book illustrated with a fictional example.

2) Every time you learn something new -- do you also make another "hello world" app to test this new knowledge? Otherwise you may get a fake understanding. Also, if you learn about cool new techniques, but never use them, you may not understand the trade-offs. By making sample applications you test your new models against the reality.

I figured android studio would be the most easy to use (where I was previously not sure how to get an app onto the phone) because its built to go with android devices.

I agree.

Unless you want to make a game, in which case Unity is probably a better option. It is not Android-specific, but it can compile to Android platform.

EDIT: Feel free to ask me specific things about Java or Android.