Welcome to the community. (Although the post is old)
My advice is to start small as you learn how to develop charms. I have two examples from my own journey that might assist you.
I encourage you also to think about Who will be using your charm in the end. Apart from you that is. Juju have a concept for the operator called juju actions which allows you to create functionality to expose to those operators which makes the process of managing your application alot more consistent, safe and secure. I highly recommend you start early to at least play around with actions.
But first, get comfortable with the juju hooks.
Good luck and hope to see your work develop.