Answer 1

Any of the above. Which one are you planning on using/focusing on the most? I'd start with whichever one will be the most useful toward whatever your goals are in the short and long term.

I've only recently started learning Kotlin, and in terms of difficulty, it's easier to deal with than Java. However, it's built upon most of Java's technologies, so it wouldn't hurt to know/understand Java prior learning Kotlin, but is hardly required.

If it were myself, I'd probably learn Java first and practice it, and then pick up Kotlin. If you plan to do a lot of work with web development also, then picking up Javascript after you learn HTML/CSS is an excellent idea also.

In the long run, you'll probably end up learning all of those languages. Java is a good place to start though.