The single most helpful volume is certainly Volume 1. Focus on the tillering chapter and the design chapter. Following that, Volume 4 is the next most helpful as far as getting started making functional bows. They both have good simple starter designs and plans detailed. All volumes are excellent and worth having, but 2 and 3 tend to focus more on specific designs and adaptations and whatnot rather than on the construction/tillering of a first or early selfbow.

“Ishi and Elvis” by Jim Hamm is also good. While not actually a “bow making” book, it does offer, as part of the story, some account of working with Osage.

There are lots of others, but I’d say that TBB I and IV are the best starting points.