Task completed!
I now have a responsive* and easy-to-use tool to help me and my colleagues lay out crowd barriers within our designs, using a spline to draw the queues.
Spline points create position for the posts (yellow)
Belts automagically connect between all posts (blue)
Toppers are added with a control for spacing and separate control to twist them (green)
The brackets that hold the toppers appear with the toppers but do not rotate, always sitting correctly on top of the posts (red)
Thanks again to 3dRaven and Kokku_RafaelDias for your help!
*For reference, when combining the various BPs, overuse of For Loop nodes was slowing everything down, making it sluggish to use. By removing a single redundant For Loop node and using outputs from an earlier one in the script, everything sped up like 100x!