New member with a new pup

My name is Alyssa and my new puppy is a Collie/Pitbull mix named Rosco. We live in Northeast Pa.

Rosco is only 7 weeks old. He was the last of an accidental litter and about to be shipped to the pound. He just came home on Saturday night and already learned sit (hand gesture as well as verbal que), sleeps through the night without waking to go to the bathroom, is almost accident free (he even whines at the door when he needs to go), and settles when he is told. So far he seems like my dream dog.

I'm wondering if anyone here has ever owned or known a collie/pit and what they were like full grown. Size and temperament. Also, will he stay this well behaved or is it just a puppy thing? I've only ever had older rescue dogs so this is all a little bit new to me. Any advice or suggestions would be wonderful.

P.S- I know both parents. His mother is a petite, mild mannered, very friendly "purebred" Rough Collie. His father is a short, stocky "purebred" blue nose. Some behavioral issues due to nervousness from previous abuse, but still a sweet dog.