Look for the resources you want, the more the better.
Study how they draw the bodies, composition, copy them a lot then try to do some originals and see if they look "medieval" enough for you.
From what I saw, there is almost no background, character are on the same plan and there is a limited number of poses.
For color, i think watercolor would be nice.
I don't think you will find any tutorials for drawing exctly like this tho
