The Mahjong Huntress

You do NOT need to get all stars that exist in the game.
In total there are 183, so you can skip 3.

My recommendation would be to skip:

1. completing chapter 5 level 3 (Backstreet) and chapter 6 level 3 (Upper deck 2) without power ups, since you cannot brute force these levels with crystals and
2. to skip getting 250 red crystals on the last boss since this is incredibly luck based and quite hard in general.