Hi Welcome to YT! and Congrats on your new baby.
Your baby is very young, he should still be with his Mom and litter mates until 12 weeks old...Puppies learn Socialization, bitting inhabition, they learn what is acceptable and what isn't from Mom and littermates.
I would not wait to get him to the Vet...I would get him in today.
You need to have food/water out for him 24/7...feeding 3 times a day is not enough they need more...thats probably why he is eating his poop...puppies burn a lot of energy they need food 24/7 right now...very important to keep his sugar level up.
I wouldn't go by what your breeder said, she did sell a 8 week old pup...not a good breeder IMO but whats done is done...and your puppy is going to need a lot of sleep right now very important. I wouldn't let him play anymore than 15 to 20 minutes.
Good luck with your new baby
