Just passing through for the moment, sorry! Hesitant to join an advance RP when I've been out of the game for a long time.
Plus, there'd be a lot of lore to get through.
I'll ease your mind a bit if you don't mind.
1. From my experience, CAH is a good rp to shake off the rust. Namely all the players are understanding, compassionate and creative as hell that it's less concern and more fun. If you were ever going to join an Adv, I recommend this one.
2. As for the lore, none is set in stone until it makes it to the IC. It's also mostly player created and flexible, making the evironment rather friendly with new players. All the important and notable stuff is in the OP, and laid out neatly for easy understanding. In addition you can add your own and build upon the world we've created.
I suggest talking and getting to know the players before fully making your decision. Mainly to see how you mesh and what the rp is like. It can't hurt after all and we're all pretty friendly with new people from talking about our PCs to making requests for matches between different individuals to random topics.