Through-hole NeoPixels are pretty simple things. There are 4 legs -- one power, one ground, one data and one data out. In this build the outer shell of the 8 is made from brass rod and grounded. The inner o's are at 5V and the power connectors from all the leds are soldered onto these.
The data out and data in of adjacent LEDs are connected with one being global data in and one being global data out (these are broken out on brass rods).
I had to add a couple of 10uf capacitors to get it all working. Currently, there's no microcontroller in there, so you have to connect it up with crocodile clips. I might do a future build as a data display with integrated controller.
I've tried building this a few ways. In the first version, I held the LEDs in place by poking them through a piece of paper. this sort-of worked, but was fiddle and error prone. For version 2, I 3D printed a jig to hold everything in place. Unfortunately, I'm not 100% sure where I put the design files for the jig, so can't easily share it.