I can’t think of good stories to read. The Dark Knight Metal series isn’t on Dc universe yet so I’m still waiting for that and I’m getting bored
What DC characters and franchises are you interested in? Recommendations can come forth once we know what you like.
By the by, the tie-in books that detail the villains of Metal are in the Comics section. That’s something Metal oriented at least.
You can prep further for Metal by reading Scott Snyder’s Batman (2011) and All-Star Batman.
Read the origin issues for all the dark knights before you read the actual dark knights metal series. Other than that I highly recommend Batman HUSH if you haven’t read it. Court of owls, the long Halloween, Batman year one, Killing joke, all star Superman, Batman rebirth, Batman speeding bullets, all star Batman