Re: GSD owner pros and cons
It sounds like you have lots of experience with raising dogs and are very involved with them, so it sounds like a GSD would be a great fit! Keep up your research (I wish I had the knowledge I have now about GSDs when I got my GSD... and I'm still learning!) and feel free to post more questions on this board. I'd say this message board and the member's responses to my questions have helped me the most with raising my dog, training, etc.
Some of the cons of the GSD are, like stated above, the amount of shedding!! Also GSDs, like most large breeds, are prone to hip and joint problems. GSDs are VERY active and need lots of exercise, mentally and physically. If they aren't challenged and exercised regularly, they can become destructive, because they need something to do with their energy. It sounds like you wouldn't have a problem with that, since you would like to take them on hikes, walks and work with them in obedience and agility. And with your 3 other dogs, the GSD would have other companions to play with and wear eachother out. If you have the time and energy to dedicate to the new GSD, as far as socialization with strangers, kids, other dogs, new situations (camping, friend's houses, etc), then it sounds like the GSD would be a perfect fit for you!