he went right up to a boxer in someone's backyard(chain length fence)...Boxer was barking, running, etc. he stood there with his tail pointed out observing, He eventually started barking after some time. I kept getting his attention and trying to distract him.
Dogs initial response was good. You waited too long until your dog made an aggressive response.
Quick flick of the leash and be on your way. Let the dog know you are in control. Don't get caught being a novice observing everything. Keep moving. Don't give the dog a chance to start barking or acting insecure.
Easier to not let dogs 'socialize' on leash as it can cause leash aggression. When people come up to you with their dogs on leash, politely avoid them. Same with children to rub your dog.
Check out the Tyler Muto videos for leash work and some easy tips to control the dog.
Tyler Muto - YouTube
Using these techniques you will develop control on leash and it'll be easier to deal with other dogs on walks etc.
If the dog is being intimidated and developing reactivity at the breeders don't bring him there. Be your dogs guardian and guide and let him know aggression is not allowed. Protect it until it is older and able to deal with bigger dogs.
The less aggressive situations it gets into between now and when it fully grows up the better. It will then know how to avoid fights but still show his strength. That's socializing for me, a dog with confidence not afraid of other dogs but also not wanting to fight other dogs. It can go up show its strength and have a sniff and walk away after. With males they will exhibit aggression as there hormones kick in at different times. You just gotta steer them through it.
I'm also a fan of Cesar Millan and read his 'Cesar's way' book. I think that is a good read for a beginner.