Selecting and creating lines of three points or more

Hello all,

So I have literally been trying to figure this out for hours..... to no avail. Basically I want to draw straight vertical lines only when two (or three) or more horizontal planes meet at the x,y - irrelevant of the z.

To do this, I re-constructed all the points with zero Z and now I am trying to create a list where the amount of times each point appears is list next to the points index number, with the eventual goal of using that to create a cull pattern and selecting only the points I want. Any ideas?? THANKS!