There's an Arrowverse thread but that's about it - http://gamrconnect.vgchartz.com/thread.php?id=227692
Also we have a list of Official Threads here: http://gamrconnect.vgchartz.com/thread.php?id=225355 for future reference, it can be found in stickies.
I dunno. I'm vaguely interested but no way I'm catching up on like 20 seasons worth of shows.
The good thing is, you don't have to. Even though you'll get the best experience if you have, it's very self contained. The last season of arrow is like a prologue to crisis so you can watch that. Other than that, you can enjoy the crossover as is.
Just a guy who doesn't want to be bored. Also