I used First Aid for a reference, but found it of very little use as a primary source for Step 3. I used usmleworld.com for the multiple choice questions and usmlesteps123.com for the ccs cases. I have no experience with Crush. I passed but not glowingly (not that I'm complaining!).
Just my experience. Ask 10 people and you may get 10 different answers on how to prepare for this exam.
Good luck!