Yes, we are allowed to place it on the border. Behind it there is only forest terrain. So no one who would be upset about a few centimeters less.
Just for understanding, you are higher than the forest?
I mean, our neighbor did it as described in #9. Foundation, above that "built" with shuttering blocks. In my opinion, he did not properly finish the wall crown, but you can probably do it better . Fence posts can be anchored in the wall or screwed on the side.
An advantage of the shuttering blocks is also, in my opinion, that they can simply remain standing. A formwork made of OSB boards or construction timber would practically be waste afterwards. That would be a shame. And also additional work/effort with ...