After a Year of development, I've discovered access to the layout is key. To do this, a 24" isle was added around the perimeter of the layout. Unfortunately it will change the interior of the layout to a single peninsula, but I believe (as my knees and back rejoice) it's worth the redesign - particularly at this early stage.
Here is the new lower layout. There is still plenty of yard storage and the service yard has been moved to the south
Initial mock-up for modular construction of upper levels
North Esat - Future Helix
Using recycled Denim Furniture padding - cutting the fabric into shapes and strips