Confusing free as in freedom with gratis there

I'd start with internal services first before opening yourself up to the outside, starting with Jellyfin possibly. Docker is worth learning as it's agnostic to the system you are using and helps with prototyping/testing quickly - something invaluable as you learn and make mistakes in your journey. From maintaining the fun stuff, such as your media service, you'll learn the other stuff, like ssh keys, Reverse proxy &c: Iterative improvement is the game when it comes to your homelab and yourself.