A 7.5 month old puppy is like a 14 year old human boy. That's the time when adolescence in dogs begins. Your puppy will become more agile and alert. He'll start marking his territory by peeing on pillars, tires, trees, etc. He'll also become very protective in the sense he may challenge other dogs in the street by barking. It's like a rivalry between two males.
This behavior is very normal at this age. If your dog gets distracted by other dogs in the street, I wonder what's wrong in it! He's also a social animal who wants to explore his surroundings. He also wants to know his fellow mates.
When I take my dog out, I allow him to sniff the grass, I also allow him to mingle with other dogs ( both domesticated and stray as long as they don't have any skin disease . He also sometimes pull but whenever, he does it excessively, I simply stop and wait for him to come back to the healing position. Sniffing is no offense, you should encourage this habit as long as it's not filthy. You should set up a time limit for him to explore his surroundings. If he's sniffing the pillar, let him do this for 10-15 seconds and then tell him-'ok that's it, time to go'.
My way of training the dog is - taking my dog on walk is just like I watching my favorite movie or hanging out with my friends. I won't like anyone to tell me which movie I should watch, what should I eat, etc. Similarly, if you want your dog to enjoy, give him a little freedom. Let him explore his surroundings and let him what he is- a dog.
Also, you are bound to have problems if you see your relationship with your dog as that of a servant and master. Your relationship is bound to be stronger if you see your relation with your pet as that of two friends.
Sarbjit, how does it matter if your dog comes out from the gate first? I don't think by doing so he's being dominant. No. He's just being a kid who just want to go out to play and he's enthusiastic. That's it.