Introducing a new Dog into the Family

Hi everyone -
I have a bit of a dilemma. I have a rescued dog named Cha Cha who has gone through a bunch of trauma, and is now quite successfully rehabilitated with one exception - he does not get along with other dogs, except for one poodle who is his only friend. He attacks other dogs at the dog park, he bullies my friends and family's dogs, and he hates children which makes it hard to go and visit my neices and nephews. My son is already 17 years old, so he isn't a bother at all to ChaCha.

Recently, I have been considering getting another dog to add to our family in the hopes of providing some socialization skills to Cha Cha so he can know how to act around other dogs, and possibly have a loving companion. I am scared though, that Cha Cha might actually harm the other dog, even though Cha Cha has no teeth since they rotted out at the puppy mill from where he was rescued. I was thinking a puppy so that the dog does not have any issues when dealing with Cha Cha from the beginning, and he can't form any resentments? I don't know, I'm sort of confused, but I would like to address the socialization issue.

thanks for any advice!
I will post photos of my Chacha.