Advice on potential dog and cat living situation...?

You may have a bigger problem here than you think. Consult a trainer and introduce the dog to other dogs and cats so that the GSD can become acquainted socially with other animals. If dogs are a challenge, I hate to think of the cat and the dog together without some one being there to keep track of their relationship with one another. Good luck, but expect anything in the beginning. Your dog HAS to be socialized and FAST !