Chewing starts off with an itch. I've heard that endorphins are released and then it can become a habit. You need to address the itch and then address the chewing.
If this dog is a poop eater and a chewer, I would think that he has nutritional issues going on. What do you feed him? I would put him on a no Chicken, no grain diet.
You can give him some Benadryl and you can put hydrocortizon on the area he chews. Given that he is a Toy, I think you are going to want to talk to a vet about correct dosage.
Next, address the chewing. I would use Bitter Apple and an Elizabethan Collar if I needed to.
Finally, poop eating....
I have to ask.... was this dog purchased at a pet store? Anyway....Don't allow him access to poop. Put him on a leash every time he goes potty. Pick up immediately afterward. Some people put MSG, sold as Accent in the grocery store, in their dog's food. As it passes through the body, it leaves a bad taste in the feces.