1) => topic15-1690.php
2) coz there's no combination left to add strikes, so the only way to add strikes is to do combo
3) usually, you can do decent enough volleys with Net Presence at 60%, Volley FH & BH at 50% & Smash at 40%. If you want better skill, you can try to lower your rally strike, but it'll get pretty tedious when you play from the baseline.
4) center well the ball into your racket, and don't step too far from the baseline.