Oh don't get me wrong. You do want to socialize him allot, but maybe give him a break from so many dogs. There is more to socialization then meeting dogs and people. Different areas, different walks, different trees and bushes, even the difference between day and night. He is taking all that in right now.. No you really don't want to Pop him on the nose. Your hand should be good things not bad things. You could let him know your serious in your voice tone without hitting him. If he keeps going on, get him out of there, and introduce him to something else. Take treats and praise him for good behavior.
"A House Is Not A Home Without A German Shepherd"