Well the biting won't stop magically, you have to teach your puppy what is and isn't acceptable. If you don't teach, then the biting probably won't ever stop - I mean, how will he know?
You can go the route of never allowing any biting/mouthing at all (which you'd achieve by telling him 'no' or 'no bite' or whatever, and ending playtime when he starts to use his mouth) but generally it is best to teach your pup bite inhibition. Same method as above, but playtime ends with a loud squeal of 'ouch!!' from you when he puts any pressure into his bite. That is better than not allowing him to use his mouth at all because it also teaches him about bite pressure. And if you're ever in the situation of an accidental or warning bite from your dog, chances are it won't be a serious one because he knows about exerting pressure with his mouth. Do a search on 'bite inhibition' or 'soft mouth' for more info.
As for the growling and snarling - well, actually that will probably never stop. Boxers are veery vocal dogs. If it's a real issue, you could train your pup to be less vocal, or more accurately, how vocal he can be by the same method as above. Playtime ends when he gets too carried away. He'll soon get the idea
