I really wouldn't call humping aggressive behavior, it's dominant behavior, but that's not the same as aggressive. He will probably hump a male or female, it doesn't matter, he will want to show his dominance. You can teach your puppy that he is the dominant dog, by setting his bowl down first. The first dog usually is the dominant dog, but some will give it up to an especially dominant newcomer. I would find the best breeder I could find, and meet the puppies. If I had a female, I would probably get a male, but since you have a male, I think you can choose either. I think one female per household is a good rule of thumb!
Because he was neutered late, much more testosterone got into his body and brain, and while his body isn't producing much new testosterone, he still exhibits some of the effects of the early testosterone. Testosterone, is one of the hormones responsible for dominance, and humping behavior.