Al stohlman books I suggest are
"The art of stitching"
"Leather tools, how to sharpen them how to use them"
These two books alone are pretty invaluable and retail for less than 30 bucks for both.
I highly suggest starting with bracelets. You can use veg tan bellies that are cheap. You will develop a lot of basic skills doing bracelets. You can practice cutting, casing, tooling, staining, antiqueing, stitching, snaps, rivets, eyelets, burnishing and finishing.
And if you mess one up your out .75 worth of leather. Someone suggested not long ago to pick one thing and get good at it, then move on.
And then start working into the bags with small cases.
Al Stohlman has has three volumes on cases.
Good luck.