WELCOME to YorkieTalk JanPan
I love the name Hustler. I have a different perceptive about pups than many people here. It sounds to me like Hustler loves you MOST! Yorkie pups play rough.... VERY rough.... at least mine do - and I love every minute. In time he will settle down but for now he is going to play. If the biting is really a problem here are a couple of things you might try.
1) when he bites too hard, quit playing and ignore him completely and entirely for about 5 minutes -- that's about as long as he will be able to associate biting too hard and not getting your attention. You could also put him in "time-out" for 5 minutes.
2) you might also have a spray bottle handy and give him a good squirt with plain water when he bites too hard -- combine this with a firm "NO"
It sounds to me like you are a terrific Yorkie Mom -- good luck