Unfortunately, Pluto's window for maximum socialization is already closing (ends around 10-12 weeks in most German Shepards), so really for the next couple of days, you want to expose him to as many dogs, people, sounds, floor surfaces, types of clothing, etc that you possibly can. To specifically answer your question, any type of dog you want him to interact well with in the future is a good type of dog to introduce him to this weekend. Make sure to have lots of yummy treats and leave the situation if Pluto is scared of something, but short of scaring him, expose him to everything! Good luck and enjoy your adorable pup!