Thanks Cynthia - so glad you think it works!
Thought the composition was a little risky starting out (those horizontals potentially leading off the right end of the canvas...) but hoped to counter that by keeping the strongest contrast/highest values at his face and hands, and pushing the values down, in the background. If I could have gotten away with making him left-handed instead of right, I'd have preferred the mirror composition so that the horizontals led into the painting rather than out!
Thanks again!