That's great- and it sounds like the dog is drivey once out of the home, just calm in the house (the enviable on-off switch). My first GSD was a treasure like yours, unknown pedigree, beautiful, no health problems perfect temperament. High energy outside the home, calm energy in the house and absolutely terrific with small children.
Sometimes I wish I'd bred her, many people stopped me and asked me if I was a GSD breeder, or where I got her, because she was such a perfect example of a balanced GSD, and unfortunately there aren't a whole lot out there in public.
Congratulations, he is beautiful.