Your posture is determined by your arm swing. If you swing up and down on a two plane swing then you should stand more upright. If you swing your arms around on a one plane swing then stand more bent over on the balls of your feet.
Cocking your wrists on the backswing creates a tremendous amount of power that is imparted on the ball when the wrists uncock at impact, you can do this three ways, early, late or swinging, see which works best for you
To implement changes swing with no speed to create a new feel