The foundation & drive building can start in early puppyhood with tug games & motivational obedience using food or a toy. Confidence building is good, though the right kind of dog is naturally self confident.
And no, not any GSD can do protection work. It requires the right combination of genetics & training. The dog has to have strong nerves, which are inherited along with sufficient drives. And, you have to work with a responsible ethical trainer.
Too many self proclaimed "protection trainers" shouldn't be in the business.