Eyber, I would not rely on Pawnee as a primary variety unless you are prepared to spray the trees to control fungal diseases. Kanza is highly resistant to scab so is a much better variety if grown without spraying. I suggest planting primarily Kanza trees because this will result in a lot less difficulty in later years.
With regard to the distance apart, 15 meters between trees will result in much more reliable production for more years. The problem with planting at 15 meters is that early nut production will be limited. This applies until the trees reach about 15 to 20 years old. From that point forward, nut production will be higher with the trees spaced further apart.
For thinning trees, they should be planned such that at least 1 pollinator tree is retained for each 9 of the other variety. Any ratio will work 1:9, 1:6, 1:4, 1:2, or 1:1 so long as you don’t go higher than 1:9. So for example, planting 10 Pawnee and 10 Kanza would be 1:1. Planting 1 Pawnee and 9 Kanza would be 1:9.
The long term goal is to reduce the number of trees gradually so that they wind up with about 25 meters between trees. You could do this by planting initially with rows 14 meters apart and trees in the row separated by 10 meters. Alternatively, the rows could be 12 meters apart and in the row spacing also 12 meters. Over time, remove every other tree in the row, then eventually remove every other row of trees.