Is there a useful book or guide that covers all U.S. halves, or do I need to buy one for the Seated Liberty, one for the Barber, one for commemorative issues, et cetera?
Redbook. But if your looking for in depth information I'm guessing a different book will be useful for each different type of coin
Here; http://blog.davidlawrence.com/ Right side, about 1/3 of the way down. Not everything, but should be a decent (and free) start.
It really depends on how deeply you want to get into it. The Redbook is a good overview but if you want to really get deep into them you're talking something like eleven books. One for the early halves, six for the seated Liberties, one for barbar, One for Walkers, one for the Kennedy, and one for the commemoratives. Somewhere around $550 to $600 worth. Maybe more. I can't find the Seated Liberty books so they will probably be high when I do.