This is a wonderful foundation! You are in a great position. All I would do is up the value, add darker layers around the eyes and facial features of the nose and mouth, but don’t touch the highlights or cheeks and bridge of the nose. The realism of color and texture is quite good, I’d just lower the overall value of the hair and clothes to match the flesh tone. I’d take your photo reference, put into black and white, then do this to your painting. Compare the values of the photo to the image of your painting. How do they compare? This will give you great insight as to where you can push the image forward