Regarding perimeter wall mock-up, I think some of the 'closed' feeling comes from the unbroken blank walls. Once some other elements are added, like the windows in the main structure, the entry door/gate in the outer wall, and the small corner tower, I think it will feel much more open. If it still feels 'closed' you could try lowering the height of the outer wall, or changing it to be more visibly permeable, possibly like a wrought-iron fence.