I have never come in contact with a pit bull/shepherd mix but my experiences with certain mixes in general is that you need to be aware of the qualities of each breed and not just how they look. For example, GSDs in general are highly vigilant, task driven and energetic. Combine this with the terrier qualities in a pit bull and there is potential for serious hyperactivity (this is a generalization, each mix is going to be vastly different based on the amount of each breed in the makeup).

There is no such thing as a free dog, you have to factor in vaccines, spay/neutering (if not already altered), toys, crate, things of yours that they are most certainly going to chew up, bones, etc. You also obviously have to think about food costs, I feed my dogs Taste of the Wild and it goes for about $50/bag (the big one, I think it's 40 pounds) and this lasts about 2-3 weeks for two medium-large size dogs.

In my experience, pit bulls are great apartment dogs. As a rescue, we do not require that applicants have a fenced yard like many other groups do. As long as your dog gets regular exercise and has plenty of toys to occupy them it should be alright. That being said, I would highly recommend that you buy a crate and crate train your dog for when you are gone. This will not only incredibly speed up the house training process if they haven't learned yet, but it will also reduce anxiety and chewing in the long run.

When introducing the two dogs you need to make sure you do it in an open, neutral area where neither dog feels cornered or pressured to face the other. It is highly advisable to have them both off-leash in a large, contained area and allow them to dictate how the introductions take place. In our rescue, we do not adopt out a dog to a home that has another dog of the same sex. Especially if one or both of the animals isn't fixed, this can lead to aggression and attempts to assert dominance.

These dogs need all the help they can get when it comes to ensuring that they are raised and trained in the most effective, supportive environment possible. It is crucial that you do not put them in a situation where something could possibly go wrong, this includes no off-leash dog parks, no leaving them outside while you're not watching, no leaving them alone with small children, and no introducing them to other dogs while both are on tight leashes.

I would suggest checking out BadRap.org's training and resources page as a good starting point to becoming educated and prepared for the breed.