Here are the brush settings I use for painting anime style cloud. The values in the settings are not essential, you do not need to follow exactly like what I have. Just play around with it, and find one settings that you prefer most.
No custom brush are needed, just tweak the default chalk brush from Photoshop.
ArtworkSome artworks I did using similar method.
ReferenceDeviantArt Anime Cloud Brush Settings
DeviantArt Blue Evening
DeviantArt Football Field