Gotta say, these are characteristics that lots of people want in their GSD. This is what the GSD was originally and what some enthusiasts are trying to keep alive. He perceives threat and wants to protect his territory and his family. Great. If your lifestyle isn't in need of that, then by all means neutralize the behavior or tone it down best you can. But it sounds like you have a good dog here. A dog like this needs some training and needs to look to you for the right moments when to express aggression. That can be done with the right trainer/training.