I started out with a photo reference, and then let the work evolve from there, with the fireflies and the night time scene happening sort of intuitively. The fireflies just happened by chance, when I found a firefly image online while looking for forest and tree photo references. When the fireflies came on, other issues like whether to make it day or night, and whether or not to include a sky became more clear. They solved everything! Fireflies are great, I tell you.
Have a great day,