1) For my game books, I use bookshelves that are from furniture stores OR are built into walls- the wood is a bit thicker & sturdier and does not bow...that much.
And to clarify, when I say "not...that much" I mean you have to look at the shelves from the side to notice the curvature.
For the nicer ones that will have a heavy load, I used 3/4" plywood with a 1" strip of poplar running down the back edgewise for support. Then some are 3/4" MDF with 1/2" wooden dowels into studs as extra back support.