aggressive dog behavior

Well, you need a muzzle to start your training, if the dog is that bad. That way if he lunges or tries to attack he can't bite. I suggest when walking him if he starts acting aggressive towards anyone, turn around immediately and walk the other way. Once he is calm turn back around and try walking him back towards what ever caused his aggression. Note this will take time and patience. Once you can get him to not lunge or growl while waking by people and dogs, then take the muzzle off and see how that works. Keep in mind that you should have it with you just in case.

Adult dog socializing

At 5 years of age, she's pretty much set in her ways. It will be a miracle if you could get her to like everyone after socializing her. Usually, that has to be done when dogs are puppies. During that first year of their life all their traits are getting fixed.
Hey! After almost 6 years of socializing one of my mutts, I just got him to stop chasing the mailman!!! And that's after going out with him every time the mailman came and act happy and give him a cookie and chat with the mailman having my dog with me. At least once a week for the last 4 years... Some dogs are extremely hard headed.