Carefully study the color sense in the examples you like. The first thing to not is the flatness of color. In the pieces you did, you included some shading, especially on flesh tones. Think flat. And don't think so literal. A person needn't be flesh colored.
Perhaps the most important thing to note on the examples is the asymmetrical design and the large sense of space. They are, in fact, a good example of how one can balance objects with space.
And, yes, for the most part, the examples lived part of their lives in Illustrator.