Very interesting. So, this is a visual that is not really an object ... or does it turn it into a combined object? I am curious in part because I used to work primarily in 3D, sometimes starting in 2D and then extruding the shape into the third dimension. I suppose this project is likely to stay 2D, but I am still curious about the implications.
To clarify, I am not sure exactly what you mean by "Leave the outer spline open (use Finish)."
For me, the walkways in each quadrant tend to terminate on the main paths, so those places are straight lines. So, I draw the spline for each of the sides and then join the ends with straight lines and use join polyline to make the whole into a single entity. Does "use finish" imply something easier?
For the inside, there are no straight lines, just one curve and so I draw most of it and then click to close it.