To drive a Nixie, you need about 170V DC on the anode. The Digits are then Controlled via GND potential. (+170V at the Anode and GND to a Digit, the digit will glow).
Though, you need a high voltage source for the anode-voltage and Driver module will probably demultiplex a 4-bit binary Input to your Digits from 0-9.
Hey @TheDarkness38, welcome to the forums! I am the author of the blog post you linked, and I’d recommend, if you have ordered the exixe drivers, that you follow the schematic under the Electronics heading in the blog post. The schematic shows exactly how to connect the exixe driver boards and as @BlackTigraC20XE suggests, you’ll also need to pick up a 170VDC power supply that runs from 5V. They’re cheaply available on eBay.
@TheDarkness38 sorry I don’t have any dimensions or CAD designs for the box as I pretty much just made everything to the size of the components that needed to fit inside. You can see it’s about 1 Raspberry Pi 3A and 1 Geiger counter wide Keep us posted with your progress building