At 12 weeks old I wouldnt at this time be too concerned. You often get mouthing with puppies. That said you need to ensure this doesn’t become a habit.
A dog will use its mouth to investigate things, like a hand. With its sibblings each would be nipping and tugging each other and its also part of the pack hirachy.
A firm “NO” should hopefully suffice and I do not recommend using any foreign objects, certainly in the first insatnce like shaker and water bottles.
Get a good trainer, with both of my dogs I worked with an animal behaviorist. Probably more expensive than a “dog trainer” but it teaches you how to understand your dog, its behaviours and what you can expect. It also teaches you a set of methodologies for training rather than just “teach it to do this or that”.
Socialise the puppy as much as you can, this time of year country shows have little companion dog show where he will meet lots of dogs. Take him in stores while hes small enough to carry. Most pet stores let you in all the time.
Developing a firm and consistent command structure at an early age is key and your tone says alot more than the words. Firm when its naughty, soothing and playful when its good, usually rewarded with a treat for achieving something on command.
Take small steps and learn to work with yor dog and train yourself to understand it and traning it will be a lot easier and lead to a long and fulfilling relationship.