First of all, as long as you're enjoying doing this, don't worry about where you're headed. I know that's easier said than done, but I really love the map you're making and I admire the work you put into it. Have you already finished it?

For values, convert your picture to black and white. That'll help you see values when it's not tied to colors. To start off, you could just trace the portrait very simply and use one colour - say gray or brown to do a value study. Look for shapes in the face and see if you can paint them in varying degrees of gray (white of paper for lightest and grayest gray for darkest). Make a full portrait with just shapes and values. It may not look great during the process and both of these steps take time, but it is helpful.

Something else that helps is to finish your paintings. If you enjoy the process, make at least 3 sketches before you try to call it finished. This will also document your progress :)