I’m going to be the first here and tell you to form your own opinion on the community. Argent Dawn has many people who are all entitled to their own opinion on many things, and the PCU is no different. Perroy no longer leads the community, though.
In regards to what it is, PCU stands for Perroy Cinematic Universe. It’s a community of guilds that banded together to create roleplay with each other under some shared rules and with coordination between them. You can find out more about the community here.
Probably the forums or Argent Archives. In-character recruitment isn’t what it was, so you’re better off looking at different mediums there. Getting into guilds is still the same, though; you usually chat with the guild master and express an interest in joining, and it’ll flow from there.
I think this is very hard to summarise in one post, but beyond the basics of writing with full punctuation and using TRP3, I’d say the most important is to know what and where you are roleplaying. Our characters aren’t really that significant in the broad scale of things (because we have no impact over the in-game world), so it’s generally a bad idea to portray archdruids, archmages or similar high power concepts that could alter the world in a way it would affect the lore.
I’m sure other, wiser people will have much more to say on this, but I think this is one of the more crucial rules to stick to.