he needs to be socialized, do you have him in a puppy training class? the classes are more about socialization than training at his age... being exposed to other dogs, people, sounds, things. Many bulldogs are fearful of inanimate objects so the gate does not surprise me... do not pet him or say 'it's ok'... they tells him the behavior is acceptable... ignore the coworing and continue to move forward and then praise after he is past it or accepted the person.
With people, it is not a bad thing that he wants a scent before being touched -- it is proper way to greet a dog, no eye contact and let them sniff first before touching. My girl was like this, and i would just ask people to let her smell you first and then she will accept you touching her