Let me preface this by saying, I haven't actually started
involvement with any bite work sport clubs yet, but I've slowly started to drift from "wow, bite sports seem so fun!" to "I really like the bite work/working shepherd breeds and their work ethic, maybe they'd suit me better than a Border Collie for my next dog/agility" to "I want to participate in bite sports with my next dog." I've just started to get to the point in my research where I feel comfortable giving information about bite work and feel familiar with some of the bite sport/protection breeds (I looked into Dobermans heavily as a prospective second dog, even got so far as starting to look at breeders, but eventually decided there were other breeds better suited to what I wanted).
is very right, there is a huge
difference between "Sport" and "Protection" in bite work. You can cross over between the two, but depending on the sport you're involved in (for example, Schutzhund vs one of the ring sports) you may have difficulties or find you don't get scored as well (in Shutzhund particularly, the judge is looking for a specific way
the dog is doing each thing, not just that they're "getting the job done"). The biggest difference is that in the bite work sports, the dog is most often being worked from "prey drive" and the object of their drive/focus in the bite suit/sleeve/pants and not the decoy themselves. In personal protection training, you're also working off of "defense drive" and utilizing "defensive aggression". That isn't to say that defensive aggression never comes into play in sports or prey drive never comes into play in protection, dogs switch drives all the time and a dog working only in defensive drive would be a crazy dog that thinks its in danger of harm/death all the time, not a healthy, well adjusted one.
Working in sports isn't going to make a stable, well adjusted, well suited
dog more more prone to aggression because 1) you're often not working from any form of aggression at all and can choose to work primarily from prey drive all the time if you want to, 2) the dog is targeting to suit/sleeve and not the decoy themselves and is pretty much playing a big game of tug over the sleeve/suit and not actually attacking the decoy, and 3) the dog pretty much understands it is a game and not actually under threat.
That said- not all dogs are suited to bite work. If a dog is already nerve-y/reactive/aggressive or has shown it is prone to bite in normal situations (over resources like food or toys, or strangers, in defense, etc), then it should not be used in bite work sports. You want to be starting with a non-aggressive, well adjusted dog.
Personal protection dogs are a whole other ball game. You're moving a dog from prey drive to defensive drive, for one, and are transitioning to hidden sleeves vs obvious bite suits/sleeves, and then training "real world" protection scenarios. There are a lot
of bad protection trainers out there- far more bad than good ones- and a bad one can literally make a dog that kills. There are many incidences of "protection trained" dogs biting and killing people (often children). Police dogs go through training similar to personal protection training, and there are many
incidences of police dogs biting civilians when they perceived a threat that was not there, or even retired dogs biting people they live with. You may need to carry insurance for the dog, and they are pretty much a walking liability. Most people are not set up to handle them, and those that are are the ones who have a long experience working and living with bite sport dogs, IMO. I think it is something of a fantasy to train a dog in personal protection and then treat it like any other pet. You are essentially training a dog that "if you see a threat, I want you to do X Y Z" and also communicating that biting is an acceptable way to deal with a threat. Many are trained to ONLY bite on command, but that isn't always how it happens, and accidents with a personal protection dog can mean disfigurement or death for children and adults and a very, very hefty lawsuit for you. Also, in a lot of states, it is illegal for a dog to bite someone on public property even if the person it bit was committing a crime, and in some it is illegal for them to bite someone on their own property if they are committing a crime. People have been sued by would-be robbers who were bitten; not saying that the robbers won all the time and nothing was ever thrown out, but it has happened.
Personally, I do not think it is a good idea for people to own protection
trained dogs. Sport dogs are a different story because they're doing something very different. Any large dog is going to be a deterrent to criminals, especially a "scary" breed. You don't need a dog trained to bite to have a crime deterrent.
I would highly suggest you look into bite laws in your area, and see if the law makes a difference between sport and protection dogs (some do, some don't). I'd also suggest looking up bite laws relating specifically to people being bitten in public, on private property, and in the commission of a crime. It is good to know about all those things prior to getting involved in any kind of bite sports, IMO.
There are also a few different bite sports, namely there's Schutzhund, which is fairly politicized these days and is the kind of sport that if you're a good trainer, you're likely to be able to go far in with an average dog. Shutzhund is very regimented and patterned, and dogs tend to score fairly consistently from trial to trial. In Ring, the order of the exercises is random and dogs tend to be all over the place in scoring between trials. There are also the Ring sports- French Ring, Belgian Ring, and Mondioring. Belgian Ring is not something you're likely to find outside of its country of origin as the set up is not super exportable for a lot of reasons. French Ring is intense- decoys are trying to make the dog miss the bite and mess up, and are exploiting the weaknesses they see in the dog. Mondio was designed as a sort of "halfway" between the other two Ring sports and was meant to be something that any bite sport trained dog (including those trained in Schutzhund) could participate in with little/no additional training. The decoy isn't allowed to make the dog miss the bite (they still have to "catch" them) but they are still expected to try to exploit weakness, I believe. They don't use a stick in Mondio to actually hit the dog, but I think they do in French. Mondio also includes more challenges of agility than French Ring, I believe, including some very high "high jumps" and very long "long jumps".
Schutzhund seems more friendly towards other breeds, while the ring sports are heavily dominated by the working shepherd breeds (Mals, Germans, and some Dutch), from what I've read/seen online, at least at a high level. I've been told/read you can get a Schutzhund 3 with an average dog that you trained really, really well, but you're only getting high level Ring placements if you have an exceptional dog.
In terms of your specific questions, I'll answer them in a separate post for the sake of length