My dog Archer might run anywhere between 6- 16 miles a day, bar Sunday when I insist he takes a day off (which he secretly enjoys). He is WGSL, three and a half, and an intact male. He was fourteen months old before in introduced him to some proper short runs, and I built up the distances slowly with him. He was eighteen- months old when he ran his first 6 mile (10k race) and he's never looked back.
However he was out covering at least 2-5 miles every morning from around 4 months old, but not as a job, but rather with a pack of dogs as a daily morning hike which allowed him to stop and start at his leisure, play, chase, sprint, roll and so on. This would have been on grass mostly. He also swam daily. I think this foundation helped him hugely, physically and mentality.
I have no experiences with WL shepherds, and I imagine the temperaments vary a great deal depending on the line. Archer was a mellow pup and is a pretty mellow dog in general. After our morning run, which is off lead and through a variety of hilly terrains, he's content to snore under my desk for the better part of the afternoon which works for my lifestyle. He is taken out again for about 30-40 minutes in the evening by my husband for an on lead walk around he city. That's all he needs to be chilled in a home - well that and a few games throughout the day. Which is actually a fair amount of work, and he's not working line.
I don't know if females are more protective or not. Most of the female GSDs I know are pretty easy going dogs, affectionate and alert, but then so is Archer, so I don't really see the difference.
Best of luck with your decision, and I hope you post pictures of your new dog when you get him/her.