It is perfectly legal to hold onto your own ball as long as it is ruled legal. The grip for a pitcher is very important. There are several levels of loose and tight grips, find what grip works best for you. It's just the opposite for a left handed pitcher. A lot of pitches in Wiffle Ball are gripped by using the seem, like a baseball.
Some pitches are obviously harder to throw then others.
If this were untrue, all pitchers would be throwing the same pitches every game. The NJWA staff has rated the six basic pitches on a scale of 1-5. One being the easiest and Five being the hardest. Almost Impossible to throw and master The Six Main Pitches of a Pro Player Hosting and playing in tournaments for the past ten years the NJWA's staff has seen it all. There are about seven or eight different pitches out there in the Wiffle Ball world, however these six pitches are the basic pitches of a Pro player.