I have 4 month old Miniature Schnauzer who I adore. He's going through his growing stages, however all in all he's a wonderful companion.  He's not alone a lot; however, he seems more comfortable with humans than other dogs. He's not aggressive; in fact his response to other dogs varies from discomfort to protective confrontation. I pay close attention to his reactions and want to leverage his comfort zone with the socialization process. So I'm considering getting a second puppy before he turns 6 or 7 months old. I would like to purchase from the same breeder (different litter) because of the temperment she seems to breed in her dogs.  What advise, experience or suggestions do others have with one versus two puppies?

 Thanks!