so a quick look at listing of Batman titles has lots of titles...which ones are the main ones? And what's the difference between the different titles like Shadow of the Bat, Showcase, etc?

Right off the top of my head the books to keep check of storywise

Batman

Detective Comics

Nightwing

Robin (whenever he has a title) and the Titans titles (since Dick Tim Jason and Damian) have been a part of the team at some point)

Batgirl titles