Oh, I forgot one thing. Don't underestimate their ability for destruction.
There's been more than one situation where the younger one has jumped up on a chair and then lifted things down from the worktop when you'd think it'd be well without of their reach.
They're also fond of chewing things wth a familiar scent for some reason.
My other dog, though, hasn't done anything like that but find out first if he's prone to that sort of thing. It'll save you the bother (and money)*.
All the advice on this thread so far is great.
I'll just add my own 2 cents :
Enroll your new pup, you, and your girlfriend in a "Doggy Kindergarten" or Beginner Obedience Class. It sounds like you two and your pup have a lot to learn about and adjust toward each other. These classes are not just to teach "sit" and "stay." More importantly, they also provide valuable instruction and support to new dog owners on how to interact and socialize with their dog(s) and maintain a healthy and structured relationship with each other. Well-behaved dog and owner = happy dog and owner.
Build a strong relationship with your veterinarian. You can always call them with any "new dog" questions; they are obviously your best resource for medical advice, and can also refer you to a certified veterinary behaviorist should the need ever arise.