Yes! However, I'll say this: If you're using a new language that you're trying to learn, don't also try to do it for time. That is to say, take your time, it doesn't matter if it takes you a few days to do a single problem. Do try and read other people's solutions in OCaml after you've solved it yourself, or even before, if you're really stuck.

Sure, but start right now solving a few problems from previous years.

You'll want to know how to open and read a file, parse input (generally line by line, splitting each line on spaces), get familiar with data structures such as the dictionary/hash map and how to use the OCaml version. Not that you'll be competing for the leaderboard; this is more about getting familiar with the typical things for solving each problem.

Absolutely. But I suggest learning it a couple of days beforehand just to know the tooling and the language enough to get started. A cold start with AoC is quite hard.

as good as any :)