I used one small brush for this painting. The size of the brush I grab for a painting, I find, really does dictate the direction of a piece. I hold the long handled brush at the end and paint at arms length with out bending the wrist. This keeps me from getting caught up in the details throughout the painting. Then at the very end I may use the small brush a bit more like a pencil and put in a bit of detail, like here in the trees and a wisp here and there in the clouds.
With a larger or wider brush, my favorite, the painting has broader, bolder brushstrokes that really help keep me from getting to tight with details. If you look through my paintings you can really see if I used a large or small brush. Very rarely do I use more than one size brush in a painting. Not to say there is a right or wrong way, just a preference of mine.
Have a Great weekend!