I dont' know how old your current dog is but I got two puppies at probably the worst time - when she was 9 months. I wouldnt' advise that.
As for initial introductions, I'd do it slowly. By the book. In a place away from home. See how they interact. Take them on a walk together.
Attitudes change quick once they realize their new friend isn't going home.
Even if the current dog is trained well, expect to do one-on-one training. My dogs walk fine on leash when they are alone, but are absolutely berserk when together.