- I haven't had any trouble using the RN css-like styles along with React-Navigation yet, what I've been writing looks consistent between devices, but I know I'll hit that issue eventually

- My approach has been to just start making apps targeting real users, either from your own business or a client's, there are several pretty good tutorials to get started, and the people who use what you create will let you know what's important to focus on (and also motivate you to keep working!).

- The react native + navigation documentation is a great starting point, but you'll still spend a while learning so your best bet is to partner up with a tutor and work alongside them to begin with, real experience is always where you get the most value at first.

- Kotlin is in an incredibly good place right now for Android development so I believe you can skip Java at first, and when the time comes when you need to check it out, you'll find that it's quite clear to make out and write with a Kotlin background. An IDE to hold your hand is always a plus as well.

Most of all, be sure to brush up on your basic algorithms and data structures, OOP design patterns, a dash of functional paradigm tools, mainstream architecture styles, and general good practices as you tackle on new technologies and you'll find out that there's a lot of overlap of all over the modern languages that translates directly. Good luck on your journey!