If you haven't enrolled in a puppy class, I highly recommend you do so!
Labs are very mouthy puppies. They have the nickname of land shark till usually up till 5-6 months. He's going to bite on your legs and arm especially when he start teething around 4 months or so. I would stick with one type of response to it and make sure everyone in the family sticks to it. Check out this sticky for different solution people have used. He really should be ok to go out and about to places that dogs don't visit. Like a coffee shop or hardware store, strip malls, You really want to be socalizing him during the first 16-20 weeks of his life. If your worried just carry him, all these new things will wear him out mentally and show him that the world isn't a scary place.
When you put him in "time out" does he ever take a nap? When Emma would get overtried she became a pain! Are you sure he's snarling at you? He could be just barking at you trying to get your attention/initiate play.
Invite some friends over with older dogs that you trust that will play with him and safety put him in his place if he's not displaying correct doggy behaviors.