what Jamie said..... there are a lot of varieties of GSD. My oldest boy is a mix of Czech working and Amer. show. My baby is a 100% Czech dog. The difference between their energy levels is night and day. Of course, each dog is an individual. You can get a working line dog with a lower drive and a show line dog with over the top energy. That is where the right breeder makes all the difference. They can match you with the right dog for you. Look at all the different types -
http://www.shawlein.com/The_Standard/13_Breed_Type/Breed_Types.html can give you some idea of what most interests you
http://www.germanshepherds.com/forum/choosing-breeder/137533-things-look-responsible-breeder.html has some good info on finding a good breeder.
For your specific questions:
are they loyal? GSDs are people dogs. They have been bred since the beginning to work with people. They will bond strongly with their whole family, but usually have a "favorite" My Rayden will be 8 in Aug. I don't think that I've gone to the bathroom by myself since he came home at 8 weeks. He really would lay down his life to protect his family. Socialize socialize socialize.
accept other animals? it really depends on the individual dog, of course, but yes they can get along. Rayden's only problem was accepting my pet rat. I think it was the whole "rat" thing because he's never had any problem with other animals. His compromise was to completely ignore her. He is also trustworthy around the bunnies and chickens. Though wild bunnies and birds are his mortal enemies.
Some dogs, though, esp if they are really high drive, are harder to introduce to new animals. Some can never be trusted unsupervised. Again, a good breeder and a good start in life/training can make a world of difference.
Health problems - yes, they do have a lot of inherited problems, both physical and mental. again, a reputable breeder can be all the difference. They should work their dogs in some way - either on their own farm, showing, obedience, Schutzhund, agility, working police/protection dogs - again, it will depend on the lines you are most interested in what work the breeder will use to evaluate their stock. They should do health testing - OFA (or PennHip) at the BARE minimum. Health-testing won't give you a 100% guarantee of a healthy dog, but it does stack the odds in your favor.
Smart? OMG yes they are smart. However, don't confuse smart with obedient. Thankfully, GSDs are dogs that like to please their families, so they excel in obedience. If you don't give them a job and keep their minds engaged, they WILL find ways to amuse themselves. It might be by trying to herd all the kids in the neighborhood or "protecting" you from the mailman - both of which can get you a big fine from animal control. A job for your GSD can be as simple as some daily obedience or as complex as an agility title or herding.
Since this is your first GSD, you might also look into rescuing an older GSD. A reputable rescue organization will have their dogs in foster homes. They can tell you if the dog is good with other animals, kids, already housebroken, etc etc