Center should hit the QB's top hand. The laces of the ball are at the QB throwing fingers. Ideally the ball should arrive at a 45 degree angle. QB should not try to grab it before the ball hits hand. Feet should be shoulder width or less apart, toes of the QB inside the heels of the center.
Slight knee bend.
As much as needed to get good fit to the frame of the center. Weight should be placed on foot opposite of where play is designed to go. As soon as ball is received the QB should pull it into to his body. QB always seats the ball first. Ball close to the body until he's ready to make the hand-off.