If you have a well-trained protection dog, none of that should be a worry. A good protection dog should be absolutely comfortable in public situations, and can easily distinguish between a threat and a friend. A well-trained protection dog will also be very attentive to the handler: basically, you will be in full control of the dog. That's absolutely important for a dog that has been trained to protect.
If you choose to have a protection-trained dog, BE CAREFUL OF THE TRAINER YOU USE! I can't stress this enough. There are so-called "trainers" out there who basically turn the dogs into super-aggressive, frenzied creatures and call them trained. That is absolutely not true. You want a trainer who can demonstrate that the dog can easily distinguish between friend and foe, only react if necessary, and will listen to the handler. Also, some trainers use extremely harsh methods to train the dogs. Avoid them.
Be aware that few dogs are actually capable of learning protection work. A dog like that requires high drive, protective instincts, obedience, confidence and more....most protection dogs are bred for their traits over the course of generations, and come from specialized breeders. And breed alone doesn't cut it: just because you have a German Shepherd dog doesn't mean he can learn protection. The average pet dog usually isn't capable of advanced protection training. That's not to say that your dog isn't, but don't get your hopes up until you have your pup evaluated by an experienced trainer.
Good luck!