Have some more rep!

I really like the way you are approaching this. You're saying things in your first post that it took me years to learn through trial and error (e.g. mixing illustrative with textures). Everything about what you're posting and what you say tells me that you have 'the eye' by which I mean you've groked the right way of approach. Damn, I wish I had it!

On your colour map, I can't say I'm mad keen about the contour lines but they may be just there for construction and later development.

Does Gimp support photoshop filters? There are some good ones out there.