First Stage: sketching the design

I decided on wild mustangs running as my subject for the painting. Here, I've transferred the basic design to the panel, after sketching it out on drawing paper to work out the kinks. The lower dark brown shape will become the rump of a horse, and the upper shape will be a stand of trees.
Don't worry, I think I can make it work.

I searched through many many photo references, and found what I wanted for the main group of horses in the front. The others are less important, and I can just wing those as I get further along, but I've indicated their placement with the white pencil.

Should be fun! Tomorrow, we'll add some color.