Congratulations on your new little guy! I would make a vet appointment ASAP just to have hime looked at and to make sure everything is ok. He's very young and will need you to be very dilligent in making sure that he's eating enough. At 7-8 weeks his teeth are tiny and may not even be in yet, so I'd get him some canned food as kibble is going to be too hard for him to eat. Don't let him play for too long or too rough. He needs to sleep a lot, like a newborn. Watch for signs hypoglycemia and make sure that you have a tube of nutrical on hand in case you need it.
Other than that, enjoy him! They don't stay puppies for very long!
