You have a very nice portrait on your hands here. I’m glad you found the process challenging. It’s one of those things that will get easier with time.
Overall your composition and your lighting are very strong. I only have 2 recommendations. First, your subjects nose points out over his cheek. Photographers generally try to avoid this by positioning their subject’s head with slightly less of a profile position. It’s not wrong what you’ve done, it just makes the shape of the nose more prominent and generally for portraits people tend towards a flatter look (often using telephoto lenses from far away).
My second recommendation has to do with your tonal balance. You have your dark black tones and some great dark grey tones, but you’re lacking enough white to make the photograph really stand out.
One thing you might want to consider is playing around with your gamma setting in post production. It won’t work that well now on this image because it helps push the tones of the greys to black while maintaining the vibrancy of the whites (which you don’t really have in this photograph). You have the opposite: Strong blacks and weak whites.
For instance, look at the difference in these images:
Notice how the top image (which was corrected in post production) has a much more dramatic look than the image on the bottom. However, the whites need to be present in the photograph in the first place for this to work. It’s just something for you to consider in the future!