Welcome and you will learn a GSD is NOT a poodle!
Needs alot more time/training and work too! Are there any dog classes available so you can have a great start and continue on the right path?
Do NOT let him eat all he wants! He'll weigh a thousand pounds if he's anything like my girls! I only give mine 1 cup in the am of PREMIUM (no grain Taste of the Wild) and 1 cup in the pm. I may have to tweak that just a bit if their exercise level is higher (summer time with lots of hiking and training).
Sure you know to train with treats so make sure to mentally calorie count for that.
Have you been doing ---> Top Training Expectations for Puppies
keeping in mind he IS a puppy still needing tons of leadership and training from the humans in his life. Even though he may look adult he's far from that.