I would make the next bag of food adult, and change over a week as you run out of the puppy chow. The large breed puppy chow is still too rich, leading to too fast of growth and the joint problems you are seeing. Hip dysplasia is largely genetic, but both it and several other problems are worse with too fast of growth. There are several problems that do go away, simple muscle pulls, or are outgrown. Discourage jumping and other joint straining activities until 18 months old. Most of what you are doing is fine. You are giving him what dogs want most, plenty of attention and time.
It is too easy to cut too much off the dark nails. Most Shepherds make an big fuss over nail cutting. Better to take less off more frequently. If you do get bleeding, a little powered alum should stop it. I always follow up nail cutting with a nice walk.
Over weight is a big problem, much more common in other breeds than the GSD. Most of them refuse to eat enough to pad their bones. Use this guide to determine if yours is the exception or in good shape.