Glad to hear your interested in becomming a farrier, or at least the craft, I will caution you there is a huge volume of info you just wont find in one book or one apprenticeship.
Im only 2/3rds the way through my time at the Kentucky Horseshoeing School, the longest ( and most costly ) as far as I know in the states, and we use the butler book, P3, but we also trim on cadaver legs and need to test out with them before we can even get under a horse, in our setup we dont actualy shoe a horse for about eight weeks, it seems like a lot when you can be taught to nail up in a week but the school is very thorough in the safty of the horse.
if your looking for a school, I must recommend this one, we have students from around the world and the top anatomy studies in the states hands down Kentucky Horseshoeing School they also work hand in hand with the AFA to certify us students, and actualy Im in Chattanooga right now for the convention, where three of our "CJF" instructors are in the contests one of them tryin out for the american farriers team, and another doing a disection and some lectures
GL bud! if you have any questions Ill do my best, toss me a pm