Those hoses will be very well secured and shielded, I trust. I presume your picture is of things just set in place for the initial "demonstration" flame. Seeing the hoses lie close to the lower keggle puts them way too close to the lower flame for my peace of mind. As pictured, I would not want to see the lower burner lit if you were my neighbor. I don't want to see the aftermath if that hose catches fire. Black pipe is fairly cheap; skin grafts are not.
I used black pipe for rigid lines, and corrugated stainless flexible lines where needed. I would suggest connecting the propane hose at the very bottom of the sculpture, below the heat. There are plenty of rigs with pipe to be seen in the DIY section, where I learned to build mine. The Brutus 10 style gas beam is beyond my abilities (no welder), so I plumbed mine.
One thing I did not learn there, and only recent learned to my chagrin, is that Home Depot and Lowes will cut and thread pipe to the exact length you need, without charge. I spent a while piecing things together to fit with stock parts, only to recently learn that they will do this. That would have simplified my build, and might be useful for yours as you plumb it.