I love the idea of Vexel Art, but it's concept has always confused me tbh.
Your tutorial, having explained the basics, has inspired me to have a go at this. I tend to construct my portraits digitally (via photoshop) and the only vector portraits I have ever created were done in illustrator, using the gradient mesh tool - That's a whole new world in itself
However, what I have never done is combine both packages. So this is definitely on "my things to try list"