A: No different. I believe, every trainer makes his mind what he wants to achieve with his dog long before he starts his search. A true GSD is a "plasticine dog", you can model anything out of him, provided you are experienced, good tempered, cool-minded, patient and endlessly kind person.
B: I would look for smaller size GSD. They are faster.
C: SEE BOTH PARENTS AT WORK, or simply on the walk - YOURSELF. Pick the first or the second born, they would be not only healthier but also have more stable temperament. Judge human attendance, it must be costant human contact. Normally, good puppies are sold before their mother was mated.
D: It is not easy to explain behaviour of such a young puppy, but, with a closer observation, I believe, you can recognize necessary qualities. For instance, if you walk on the gass, wether your desired puppy will start following you the first, or he/she will be in the tail of the puppy train. There are a few tricks to check drives, irritability, etc.