Turning head study into an actual painting

Hi Tom, you got this! It is hard to draw human head, even harder is to paint it. Painting is a diffrent approach to from, called mass drawing, if you want to learn more about this from academic perspective I reccomend book "The Practice and Science of Drawing" by Harold Speed. As for your questions, which tool to use, it all comes with practice and approach you choose. I like to use soft brush to build cylidrical forms of the head, some specific round brush to add more planar feel, a chalk brush to add form, a soft noise to suggest skin texture. Keep on going, you have youe system to learn, that's a good thing, have fun, don;t count the hours at the beginning, you will make mistakes, learn from them, don't be negative about your work, it will lead you nowhere, accepting the outcome is part of the process. Having planes mapped out is good, but as mass drawing is about simplification, use them as guides, at the same time don't try to include every in a portrait, it will lead to overcomplicated partrait. Painting is about how you can manage information within 5 values and hue shift. Keep it up!