Sorry, thought I said. I'm pretty much working exclusively in ProCreate. It is, by far, the most full-featured illustration app on the iPad Pro that is optimized for everything. I'm using it a lot like I use Photoshop with layer modes (multiply, overlay, etc..). I do a sketch, then I'll do a solid color layer , like all the green. Then I'll duplicate it, alpha lock the duplicate layer so it protects the edges, then fill it with white and make it a multiply layer. Then I use that as my shading/modeling layer. I'll paint the shadows and shading in on that layer. When it "multiplies" the white disappears and the dark is all that shows up.
For all the textures, I used things like the "cloud" brush to make the "weathering" on the leather and some of the different water splatter brushes to make the skin textures and such.