Looking to possibly get a German Shepherd after my Collie passed over a year ago, I need tips

I really miss him, a LOT, but I think I'm starting to come around to want a dog again.

Best toys for mental stimulation for a GSD and in puppy stage just in case I get the dog as a puppy? And what are your best tips for exercise for the German Shepherds? Will walks and playing fetch and basic things like that be enough? I'm happy to hear anything you have to throw at me. I'm aware they're high energy and intense dogs, I just want to have an idea of what more they require. Thank you (: