On the Rainbow Plaid Bunny, I used 4, one for each color (Teal Mint*, Brilliant Purple, Royal Fuchsia, and Bright Yellow)
*note: I would pick a darker color than this mint color next time. It was too close to the base color.
With the sponges, do not load them with too much paint. You don’t want it bleeding through the stencil. I dab it on, you can see in the video below. This gives it a distressed look and not a solid look. I love stenciling this way because if I do have some bleed through it’s not noticeable.