You should be able to hit all the colors in that photo with the Zorn palette. First, establish the background accurately (why did you change it?). A straight ivory black/white mix should give a cool gray that’s very close to the photo, make sure you get the value right! For the complexion colors, I suggest you mix up several tints of black, red, and yellow with white and use those as the bases for your lighter mixtures, rather than bouncing back and forth between your pure colors. Identify the value of the area, determine whether it’s predominantly red/pink, yellow, or gray, and mix colors of similar value together. Color mixing is much easier if you approach it analytically rather than just blindly throwing colors into an ever-growing pile of paint!

There’s no way around it, foreshortening is tricky. You’re doing the classic thing, which is not allowing yourself to draw the foreshortened elements, in this case the legs, as short as you’re actually seeing them. Even though you’ve already corrected the length of the legs, you haven’t done it nearly enough. Now that you’ve finished your drawing, overlay it on the photo and you’ll be amazed at how extreme the foreshortening in it actually is.

Do more thumbnails. The answer to "how many thumbnails should I do?" is always "do more thumbnails." The first concept is interesting, but you need to explore your value mapping more. Where do you want us to look? I assume the center of interest should be the ship and the face, but in the first one it’s the area behind her (?) head, and in the second it’s the palm of her hand, because those are the areas of highest vale contrast, and the size/shape contrast isn’t enough to overcome that.

As everyone has mentioned, the major issues are the proportions, specifically the length of the trunk. You’re halfway to solving this since you’re thinking about the skeleton, though. If you look at your skeletal drawing, you’ll see that his rib cage is much too close to his pelvis. This is the true value of learning anatomy, as understanding what’s going in underneath the surface of the body helps you understand what’s happening on the parts we can see.

This is looking really good! What jumps out at me is that the haft of that weapon seems really thin.

It's my favorite composition/storytelling book. A classic.

READ it, don't just skim and look at the pictures. This isn't true for all drawing books, but Mike is good writer, and his text is just as important as the images.

I have some thoughts on this, would you mind a paintover?

Less writing, more drawing.

I'd definitely recommend Harold Speed's two books, The Practice and Science of Drawing and Oil Painting Techniques and Materials: https://www.amazon.com/Practice-Science-Drawing-Dover-Instruction/dp/0486228703 (Out of copyright, so also available at https://archive.org/details/practicescienceo00speerich) https://www.amazon.com/Painting-Techniques-Materials-Dover-Instruction/dp/0486255069 The great thing about Speed's books is that you can read them when you're first starting out and get a huge amount from, then go back in five/ten/fifteen years and get just as much, if not more. Obviously, since they're around 100 years old a lot of the info on materials is outdated, and his writing style is a bit formal to today's ear, but once you get used to it he's actually quite engaging, unlike, say, Bridgman. Another book I can't speak highly enough about is Molly Bang's Picture This: How Pictures Work: https://www.amazon.com/Picture-This-How-Pictures-Work/dp/1452151997 It looks deceptively simple, but it is HANDS DOWN my favorite book about composition and visual storytelling.