First of all, this will be your creation -- do what you feel is best to convey your art. Rules, guidelines, and opinions can help form what you decide; but ultimately, you will determine what works.
Second, I really like your portrait/figure. It is a beautiful representation. I also like the pose in the upper left placement on your page.
Third, I am not a portrait painter. So, weigh my opinion lightly.
To my eye and to place the most focus on your subject, it would make sense to eliminate the space below the blue "line." Then, I would take away the current white space on the right, reversing the dark brown/black behind your portrait, leaving it light. That would accomplish some white space, perhaps with a blurred background as you suggest. Something like this, perhaps:
As I said previously, do what you like -- you'll enjoy the process better if you've determined your plan rather than others.
I'll be eager to read what others think as well.
Whatever you do, please share your progress and finished work!