Okay, Sacry, but let's take one thing at a time.
First and Second: your Dobie will learn good manners around people and other dogs if you begin socializing him/her right now. Take your dog for walks where there are people and other dogs, somewhere like a park. Praise your dog for welll mannered behaviour; if he growls or barks for no reason, tell him "No" and if your dog doesn't stop, you might put your hand under the jaw or something that will communicate - gently - that this behaviour is unacceptable.
These walks are also a great time to begin training your Dobie to walk properly on a lead. With a puppy, especially, I really prefer using a harness to a "choke chain." If your pup learns proper leash etiquette, you won't have to resort to the chain even when it's grown. I really consider a choke chain a last resort.
Third: My Bimmer won't take food from anyone else, and brings anything he finds to me before he indulges (unless, of course, he's killed it hunting). I started that habit early with him by making him give me anything he picked up unless he got it from my hand or his food dish and letting me look at it before I gave it backc to him. This accomplished two things: he doesn't take food from anyone without my okay, and he's used to me messing around in his mouth.
Fourth: Your Doberman should learn to walk only with you by the simple expedient of your being the only person who takes him for walks.
As to finding things . . . try making a game out of hiding his toys and having him find them. I've never actually trained a dog to do that, but my German Shepherds have always been pretty good about it naturally.
Your dog will learn much more from you and, I believe, bond much more intimately with you if you spend a lot of time touching him and talking to him. I feel that it is very important that you talk to your dog. Some dogs understand more than others, but it really does make a huge difference in my experience.
The other advice I'd give you is to take your puppy to obedience classes. Dobermans thrive on that sort of thing. It also helps with socialization skills.
If I think of anything else, I'll get back to you.
Be sure to post plenty of photos of your Dobie; they are such fantastic dogs.