Your GSD shows interest. That's great. However, trying to turn a GSD into a border collie will probably be frustrating to the GSD.
GSD's punish sheep for leaving a graze. It's not gathering work, but forcing straying sheep back into a determined area. If your dog has any real GSD instinct in it, the difference is very conflicting, leaving the dog feeling lots of mental pressure when it is close to the sheep. That's why folks who try and do gathering work with GSD's complain about their hard bit all the time.
They are tending workers. Check out Leerburg online's video about "sheep dog" training and HGH trials.
Also, you can find some great youtube video of Ulf Kintzel doing tending style work on youtube. You can also youtube search Geary Loff's "Elite" tending an orchard.
Ulf also has a website, whitecloversheepfarm.com I think. He makes his living with sheep and tending dogs in New York.