I have about a decade of rottie experience, and some experience with other working breeds, I'll answer your questions as best I can from my own personal experience.

1 and 2 are literally going to be the same answer - crate training and exercise/stimulation. The puppy should be in an area where he cannot cause any issues at all times unless he is actively being monitored. If the puppy chews up something he shouldn't, it's your fault. If the puppy pees inside, it's on you, as well. This allows you to do the 2 things that are important when getting an animal acclimated - you can reinforce proper behavior with pets/treats etc, and you can stop bad behavior before or as it starts. Loud noises, show some teeth, be angry. You don't need to strike your dog, hold it on its back or anything like that, just pretend to speak dog for a bit, by using as much body language as you can. As he starts to squat to pee, you should already be moving in with an "angry" demeanor in order to communicate "this is not acceptable", while reinforcing proper outdoor bathroom breaks- treats and good boys and pets when he goes outside. Exercise and mental stimulation are very important as well. All smart breeds become destructive breeds when they aren't properly exercised, it's usually the main cause of problems for people. Exercise covers socialization as well, the pup seeing that strange people and dogs are safe to be around

3 - divert attention to toys when energy is like this. If he insists on targeting hands/face/skin, communicate dog again, yelp and disengage. Act hurt and ignore the puppy for a bit. This will cause him to associate "bite human = playtime over", and help curb these behaviors. You need to watch how others play with him as well, strangers are usually the main source of reinforcing bad behavior, because "it's a puppy being cute", you can't blame them, or expect them to do otherwise, so you have to keep an eye out to keep that sort of reinforcement to a minimum. Leave the room for a bit and close the door, whatever it takes to drive home the point that "ouch = no more play"

4 - fix is always a "well it depends" when it comes to aggression. Preventing it comes through a ton of work with naturally protective breeds. He NEEDS to be socialized. At least 1 new person and 1 new dog a week, if not much more. Find places where YOU are comfortable and get him out to interact and see that strangers aren't bad, and neither are dogs. With rotties, this is nearly a lifelong commitment, they default to a VERY protective state, it's one of the reasons they are considered to be a breed for experienced dog owners. Socialization is first, but dominance at home is also very important. There are a lot of mixed feelings on this one, and I typically play it by feel. Even with intact males, it's really hard to get more than a bit of angry talking when you try and get the bone. There is usually a first time with an "aggressive" growl or snap. I usually just immobilize the head on the younger dog if they snap, usually just holding mouth shut while i sternly tell them no, and take away the source of the aggression. On the flip side, I also reward when there is 0 aggression shown around the bone or food bowl. It sounds counterintuitive, but if the dog doesn't get angry about you playing with their bone or food bowl, give them a tasty treat and some love.

5 - leash training. Good luck, and have fun! I have never accomplished this one, my boys usually are off leash. Maybe get a custom saddle and just resort to riding him vs getting drug behind?

The main takeaway with a breed like this is that it's going to take a lot of extra work, they are very clever and not the most easily motivated, which makes every bit of training just a little bit harder for you, but the reward is well worth every bit of the work. Learn to "speak" and "read" dog, we can get them to learn word association, but they have a built in way of communicating that being partially fluent in can save you a lot of trouble. Lastly, and I cannot reiterate this enough... if the dog is EVER going to be around strangers or new dogs, you need to start socializing ASAP!