Planning a Formal Portrait of a Young Professional

I have been commissioned to paint a formal portrait of a young man to be hung in his office. This is something new for me - have been thinking of the best way to approach it. I don't want it to be stuffy or stiff, but it still has to look professional. There is an idea that I like, I have been thinking all night about it, even in my sleep. Having always loved the way George de la Tour uses a single source of focalized light, bathing some of the subject's features in light, while leaving part of the painting in shadow I think I will play with this composition as a playful homage. It is a bit dramatic, but I rather love the idea. As I will be taking the pictures to be used as reference for the painting I think it will be better to take them at night and see if I can create that effect with a single lamp, try different angles to see which is better. The general pose would be of him sitting in his desk, with a neutral dark background (that can be revised later), the hands on the desk receiving the same light as the face. Jacket and shirt, tie? will try it both ways, he is young, will have to ask if he always uses a tie at work - it is Florida, so there is a tendency to a more laid back work environment. It is very important that he is looks as natural as possible, the way he always looks at work.
I will post the pictures and a sketch as soon as I have them. I will be taking them tomorrow night. This is going to be exiting.
What I have found that works for me is sketching the general idea, taking the pictures, playing with them a bit to get the composition I like, then printing the one I think will work.
I like to draw with a very soft pencil on the canvas, not going into great detail, but getting all the basic shapes so as not to get lost. Once I have this, I cover the drawing with an acrylic wash in a light shade of whatever color seems to be present in most of the picture. It has lately been mostly a shade of warm yellow. This serves two purposes, it covers and protects my drawing and gives me a nice background that allows me to paint without worrying about having to cover all the white canvas when I paint, parts of it can peek as part of the light sections of the painting.. This is going to be the base for the oil painting. In the past I used to go over the drawing with oils, but as I like to begin with a thin paint,and it has a tendency to drip , the turpentine would erase my sketch - I don't like to paint without my sketch, I feel like I am flying blind, it freaks me out, I need the security blanket of a drawing, so that got me into thinking how to solve this problem.
After this is done, and it dries very quickly, I work a little bit of color in the background, even if it is only in umbers and siennas (in a very large painting I did this in acrylics too, because it speeds up the preparation process) I need to be able to paint the face and hands over a base of colour, not having to paint the background afterwards trying not to muss the face contour, just softening its borders - and it allows me to paint the hair leaving the ends loose. If I have to rework the background, then I will go over the hair again too.
Size and Scale of the Portrait
I have painted portraits in which the size of the person's head was a little bit larger than life and that DOES NOT WORK. It looks strange, not graceful, makes you uneasy when you look at it, even if you don't know why, unless you are painting a mural that is going to be watched from a great distance, It is better to go with the real size or smaller.

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