Spiral - Overall
I found it easiest to start at the top and spiral down. The first string defines the spiral and the rest just follow that. Based on my markings at the bottom each string would be 5 marks over (or screws, or vertial lights). I would then zip tie the spiral to the vertical stringers to hold them in place.
As you can see the trees started to sag a bit in the middle, although they started out fine. Next year I will probably add support rings in the middle sections (I'm thinking hula hoops).