HI there,
it would be very interesting to work on the illustrations for your fantasy book. I checked the reference image and I have an idea about the style you are after. I can offer a very similar look, but done by hand on paper. If you'd like real, custom, done from scratch art for your book, I would be very happy to discuss terms over chat. Please kindly check https://www.freelancer.com/u/ddimitrovska?w=f to see samples of my previous commissioned work. You'd understand that, given the different medium, work would take longer than 20 days.
In the process, I would first draft a storyboard and design the characters, then prepare pencil sketches of the scenes. In this phase, unlimited revisions are possible, until we are completely satisfied with the result. I would then proceed with colouring (depending on the media we choose for the book - I would suggest that a mixed medium of pen and ink and watercolours would be closest to the reference style you provided).
I'm available on chat and I'd be happy to hear from you,
kind regards,
Dusica