I understand that you are concerned that your puppy is eating feces.
While this isn't normal per se, it is a very common vice in dogs.
Many dogs are drawn to eating feces. In most cases it doesn't mean that they are lacking any thing in their diet or that there is anything wrong with them.
The foods that we feed our pets are so high in nutrition all of the nutrients aren't necessarily used and the stool may smell pretty good to your dog, not much different from food. Some animals, like rats and mice routinely eat feces as a food source if given the chance.
If he is highly food driven he simply finds feces as a treat.
It certainly isn't a great habit for him as it is a way of picking up gastrointestinal parasites and introducing more bacteria into his oral cavity.
There isn't much that you can do about his habit except not allowing him access to stools. In highly food driven dogs even a severe scolding or punishing him won't be enough to counteract what he feels is the positive reinforcement of finding a "treat".
There are products out, such as Forbid, which make the stool taste bad but this doesn't always dissuade all dogs or sometimes they only stop while on the supplement. And many dogs find the taste of the product distasteful and won't eat food with the product on their food. You can try one of these products, and they may train him well enough to stop for a while but this way be something that you may need to use on and off with him to reinforce the lesson. Luckily he is a puppy so this isn't yet an ingrained habit.
Certainly if he seems unhealthy in any other way it is worth having his veterinarian check him over and run some blood tests to make sure there isn't any illness driving his stool eating. I would defInitely recommend submitting a stool for your veterinarian to check it for gastrointestinal parasites. In most cases this is a behavioral issue, however in some dogs it is a sign of malabsorption/maldigestion or underlying diseases associated with the gastrointestinal tract , pancreas or liver. If he is especially thin I would highly recommend having him examined.
Chewing is very, very normal at this age. It is the only good way for them to learn about their environment and help with massaging gums as he loses teeth and new teeth erupt. It is very important to find appropriate toys to satisfy his need to chew. These include kong toys of different types. Here is a link to a list of approved "dental" treats and chews to help keep his teeth healthy and satisfy his need to chew : http://www.vohc.org/VOHCAcceptedProductsTable_Dogs.pdf
Please let me know if you have any further questions.