I would like to know a little more information mainly because the airfoil choice and wing configuration are a little odd. Usually a high wing aircraft would have a cambered section and more thickness. Like a trainer.
What you are describing reminds me of a shoulder wing Q-500 design. 12% is the minimum thickness for these planes, and a good example of how fast a 12% airfoil is.
What is the objective of the design? Engine size, wing area, aspect ratio? I am genuinely curious.