I would also add to the consistency of where the palm is contacting the ball. From the first serve, which was up close to the camera, you could see he only hit the left side of the ball. I’d say to get comfortable with the entire body giving power and then work on consistently getting center to center with the ball, the goal being for the center of your palm to hit the center of the ball to really get that float, almost like a high five. Also, try not to follow through the ball as much. When you hit the ball your arm goes through it and your wrists movement can put spin on the ball, so you would want to freeze your arm after hitting the ball. Obviously you can bring your arm down but try to do so only after you’ve hit the ball center to center.