Question:
We also are thinking about getting a cat.
Is it better (i.e. safer) to bring a dog into a house that already has a cat? Or, vice versa?
The only time we had a cat....we already had a dog.... I don't remember that there were problems.....
Usually there aren't, at least in my personal experiences. I do know some dogs, such as Huskies raised without a cat, will attack them. Plenty of adult cats do not accept a dog, especially an adult dog. They are more likely to adjust to the puppy since they can initially tell the pup they are the boss.
I'm sure you can find a dog & cat that will get along, just be sure to ask some questions. If you really like this dog you are having for a visit, ask a friend with a cat if they can meet (keeping pooch on a leash). You will quickly know if the dog is aggressive or not.