hi and welcome to the forums Barking and mouthing/biting are common and normal puppy behaviours. A combination of excitement and learning about the world.
Here are a couple of videos that may help with both. I can thoroughly recommend this trainer, she has a world wide reputation and it is all positive reinforcement based training. Although she uses a clicker, it is perfectly fine to substitute the click for a marker word such as yes if you prefer.
I would suggest watching the intro videos first, just to get a feel for what is being explained:
https://www.youtube.com/watch?v=_wv1uvvqaSw&list=PLXtcKXk-QWoiH-suCukjGsNiOntiFW4YK
Barking
https://www.youtube.com/watch?v=Jp_l9C1yT1g&index=4&list=PLE345355EA335F575
Mouthing/biting
https://www.youtube.com/watch?v=c77--cCHPyU&list=PLF26FD559887E7EA4&index=9
Do have a browse through all her videos. The majority are less than 5 minutes long and even if you can't get to a training class at the moment, they should give you some guidance on things to train. What I would definitely recommend though is that you find safe opportunities for socialisation with other dogs. Obedience/puppy classes normally help with this in a secure environment so you will need to find alternative ways of doing it. Dog parks are not great places for this as some people have little or no control over their dogs and a small puppy can easily be frightened by large dogs. Maybe your vet runs puppy socialisation classes/puppy classes? If so, they can also sometimes help with some of the basic behaviour skills.
What is your pup's name BTW? We do love puppy pictures here so feel free to share

In our search for a puppy who also adopted a retired mommy dog (different breeder). She is so well behaved but we had take no credit for that. We have no idea what we are doing! Her name is Stacy. She came with that name of course.
My breeder said she has never even had a Sheltie growl....why is our puppy so mean? We hold her at arms length and say no but she has done this more than once. Has anyone else dealt with this or do I have an unusual case?