My personal impression:
I played my first tournament of AA50 being a complete Noob. AA50 is my first AA-game - and starting the tournament with the “experience” of only one PBF-game finished at that moment (and I only play PBF) I had the same thoughts as you.
What I found out is that my (two) opponents were very friendly and patient. I learned a lot from these games, and my opponents helped me with some good analysis after the games.
So you have to start at a point in order to become “an expert player” in the future.
What I recommend is to watch some games in order to get a feeling for the atmosphere and the common notation. Learn the rules and the FAQ and then start playing.
You may want to try playing some other forum games before … but I personally did not have the impression that this was obligatory for joining a tournament.
Just my thoughts…
Good luck :-)