You will probably get a lot of help here. Renee has a GSD, and BigDog has gone through a lot trying to train his GSD puppy, so I am sure that he can help you too. Debi has one also, and there are several other members who have them that will be able to help you.
Have you used positive reinforcement with the training such as food? I am sure you praise him when he does good, but a little treat would help a great deal also when he does good. I have a book that I had been studying when I decided I wanted a GSD a while back. It has a lot about training a GSD puppy with the leash. The dog hooks everything in its environment to learning. The leash is a very visible part of the environment. If you train with the leash in your hand it will make a huge difference in the dog's performance when you have to remove it. So, it is much more desirable to train the dog without the leash being visible. The most efficient way to do this, and still retain some control over the dog, is to drop the leash on the ground and stand on it. So when you are trying to teach him commands, he is paying attention to you, and will not connct the command to the leash, but to you. So, if he doesn't see the leash, eventually he should listen to you whether the leash is there or not. Learning to step on and off the leash will take some work on your part, but it will be worth it. In addition to control, another benefit of letting the lead stay on the floor is that it foces you to interact with the dog rather than continually using the lead to overwhelm it. the hand movements you develop in teaching the dog into position with the food become your communication link that helps you to communicate with your dog. I know you were basically talking about walking with the dog, but it would be better for the dog to learn that you are the one to obey, and not necessarily the leash. A lot of his barking problems may be that he feels trapped on the leash and if another dog came to attack him he could not flee if had too he would just have to fight so being on the lead may make him act out and try to warn others off, you have to help teach him it is a positive experience and maybe every time before you go for a walk, praise him and give him a treat before you go. I am sure some others will have some great advice, so don't worry you will figure it out. I tried my best to help, and I hope it helped some. Having a puppy is a learning experience for both you and the puppy, you will all figure it out together and it will work, puppies can be very difficult in the learning process, but it is worth it when they are older and listen to you, and have become your best friend.