Wow. You've described my dog.
However, my dog is now a litte over 2 years old so hopefully I can tell you a little bit about what I've done and how things have progressed with us.
That high-pitched noise happens because she's scared. That's her, "You're scaring me but I am NOT backing down!" noise. At least that's what it is with my dog. That's why it's so high-pitched. I prefer that to the bass that you're looking for...after all, people see a Doberman with a menacing defense and that doesn't always go over so well - even if it IS to put the other dog in line.
Like I said, you've described my dog. She has very little interest in playing with other dogs, she likes her ball and she likes to play fetch. Here's the interesting thing with us, though...she'll play with other dogs in daycare when we're not there. She's never had an issue playing with other dogs in daycare, but when we're at the dog park, she has very little interest in other dogs. She might occasionally find one she'll play with for a few minutes but will inevitably find a ball and lose interest.
Don't let her just sit and chew on a ball. First, with tennis balls, they're NOT meant to be chewed and the glue that is on them will come off in your dog's mouth and that's not good for them or their teeth. Secondly, we've taken our dog to playgroups at our local training center since she was little. Over time she got less and less interested in dogs and more and more interested in her ball. It got to the point where she would just carry a ball around in her mouth, find a corner and chew on it if we didn't play fetch with her. The other dogs would play and she would be in her corner. One of the trainers there actually noticed and said that we shouldn't let her do that. It's like the kid who sits in the corner and plays by themselves while all the other kids play together. It's not good. It's not good for their self-esteem and the more we let her do it, the more obsessed with it she'll become. Also, it's her crutch for dealing with other dogs - it tells me that she's anxious around them. You might never have a dog that just jumps right into a group of dogs and start playing.
She carries a ball in her mouth for security. When she's unsure, she gets a ball. When we go on off-leash hikes with her, she'll have some interest in fetch, but she's usually more interested in running and exploring and sniffing. It's only in the dog parks that she gets CRAZY ball-obsessive...it's her security blanket.
Here's a problem we have now that you might want to watch for since our dogs seem so similar. At around 1 year or a little before that, she started guarding her toys with other dogs. She doesn't guard anything with people and she never guarded until she got about 1 year old. It happened with a puppy that she had played with just fine the week before. Even the week before, she had a rope toy in her mouth and the puppy had jumped at it and tried to grab it from her to play tug. She had played with the puppy and they were fine. The following week - same toy, same puppy...the second the puppy tried to grab the toy out of her mouth, my dog freaked out. It was that high-pitched frenzy of an attack. She wasn't out to harm...and she hasn't hurt any dog, but that's when it all started. Now, if she has a toy and a dog so much as SNIFFS her too much, she tells them off. That's another reason why I want to warn you from letting her get too attached to her toys. I don't have the answers as to how to prevent this but I imagine nipping that obsession in the bud might help. Unfortunately for us, we'd let it progress for far longer than you have before we learned that she was actually a little obsessed with her toys.
As far as growling and barking and fixating on people around the neighborhood. I had the EXACT same problem with my pup and I asked the same question here. People freaked me out because they said it was abnormal, they had horror stories of dogs that went on to bite and had to be put down. People told me I had to get a trainer ASAP...and I did. My trainer did a session with my dog and told me that it was fear-based. From your dogs other behaviors I have a feeling that it's the same for your dog. MY dog was a little older than yours when she started exhibiting similar behaviors but she wasn't older by much. I just have to say - don't panic!
Remember...Dobermans ARE guard dogs. They ARE protective of their home! They will always alert you to suspicious people and you don't want to completely discourage that. You WANT them to let you know when someone bad is in the area. You need to control it, though. That being said, it's important to socialize. We also learned that there's a difference between home socializing and outside socializing. Our dog is fine outside the house area. We take her on off-leash hikes with other dogs, she's fine in stores, she's fine anywhere else but she is territorial around the house. I would try to focus on socializing around your neighborhood. Always have treats on you and whenever you can, stop a neighbor and see if they will have your dog sit and throw a treat to your dog and then let your dog sniff them. Of course, if your dog has ever exhibited signs that indicate she might bite, I would maybe back off on the sniffing part. However, remember that the only way a dog truly knows someone is to smell them. For my dog, if I don't let her sniff another dog if we're on a walk around the neighborhood, that dog is an intruder and an enemy. If I'm lucky enough to be able to get them close, she will immediately stop barking, sniff, and maybe even play-bow. You're lucky that your dog is still small. Your dog is still cute. People won't be as scared of her. Take advantage of her size because you'll have far less people willing to approach a growling/barking full-grown doberman. Just explain that you're trying to teach her manners or something. Remember to have them make her sit or do some trick you've taught her before giving her a treat. Having your neighbors treat is more helpful than you treating however giving her treats when she sees a neighbor is better than nothing. If you even have a second where she's not barking, give her incredibly enthusiastic praise, treats and then take her and walk away. Try not to walk her away from a 'threat' when she's going crazy. If her 'aggression' is fear-based like my dog, she's barking to tell that person to go away and leave you guys alone. By taking your dog and leaving when she barks, you're encouraging that reaction.
Distract her. Once she's distracted for a second (focused on you), praise, treat, guide her away. You might even walk back and repeat. The more practice the better. Like I said, take advantage of her cuteness and small size now. You can control her better, you can guide her better, you're not as threatening to neighbors either.
I can't speak for your dog, but my dog doesn't bite. I know no one can say that for sure but I can say my dog doesn't bite like I can say I won't stab someone. Can I say I'll never stab someone? No...but I'm pretty positive I won't. I know this because her leash wasn't on right one time and she got off while barking/lunging at someone walking down the street. She ran up to them, sniffed, and then trotted back and didn't bark again. I can't say your dog will do the same but don't assume that just because your dog is barking and growling it means she will bite. However, don't assume she won't either...at 5 months I'd say there's still some time to get to know your dog. Also, if you can have some parties or have people over that's all good for socializing in your house and in your neighborhood. A well-behaved dog in public is different from a well-behaved dog at the house.
Also, does she have a favorite toy? That might be a great distraction for her with people. It's just about breaking that focus. Higher levels of training will also be incredibly helpful as well.
Oh...and regarding the ball/dog issue and in general...if nothing else...have a good heel, a good leave-it and a good drop-it. IMO, the most useful commands for my dog. My dog's leave-it is incredibly useful for when she sees a neighbor and her hackles start going up. Also, I'm working on a better look-at-me to help her refocus. Oh, and I've found that saying 'It's ok' to my dog when she's worked up is not as effective as giving her an enthusiastic 'good girl!' when I can catch a break between her barking.
Sorry this is so long but hopefully it wasn't horribly confusing. We seem to have very similar dogs.
Another thing I have to add. Training, training, training! The more training you do, the more confidence you build in her, the closer your bond is, the more secure and clear her world is. She's too young now but I would even do some just-for-fun classes after she has a decent level of obedience. By just-for-fun I mean rally or agility or scenting...group classes that lets her work her mind, build her confidence (especially something like agility where she's literally overcoming obstacles) and builds your bond with your dog. That's when she's a little older...for now, it's all about obedience!
