Hi and welcome to Yorkietalk! Congrats on your new baby! You will find a wealth of information here.
You don't want to take him out in public or on walks until he's had all of his shots. You can start getting him used to a harness and leash, however. Please don't use a collar with a leash as yorkies are prone to collapsed trachea. I suggest a step in harness but there are lots of different types out there to choose from.
My recommendation for the "mouthing" behavior is to remove your hand when he starts to bite and replace it with an appropriate chew toy. (keep lots of those around
) Don't yell out or respond to his mouthing verbally as that might get him excited. I thought Ginger would never stop this, but I have to say she has a very behaved little mouth now that she's all grown up.
I have never used pee pads, so will defer those questions to someone else, however for potty training, your best friend is a strict feeding/pottying/sleeping/playing schedule so that he gets into a routine and you can begin to predict when he'll need to go.
Good luck and when you can, post pics! We love puppy pictures!