It's kind of like playing roulette, you may get a good dog or you may not. You may get a dog with no health problems and you may get one with health problems. It's the main reason so many on here will tell you we went to a breeder who did health tests, know the pedigree of their dogs (the temperaments, strengths and weaknesses of the dogs behind the sire and dam), title their dogs.
Your JRT may or may not get along with your German Shepherd regardless of sex. JRTs are very high drive and prey driven, just like a German Shepherd. He's gotten along with friends' dogs, but this one will be in his house, with his toys, with his person. Or your German Shepherd as it grows may decide she doesn't want to share.
Personally I think your best bet is going to someone who is a reputable breeder who can help to pick out the pup that is best for you and what you want.