I designed the circuit to light the tubes as shown below, with daisy chained Shift Registers (74HC595) connected to the High Power NPN Transistors (MPSA42) to each cathode of the Nixie tubes so that the high voltage could drain through the tube, through the transistor, and to ground without frying the ATMEGA chip I am using to control it. I will connect all the cathodes of each Nixie in parallel (tube 1's 5 connects to tube 2's 5 to tube 3's 5, etc.), but the anodes to separate control circuits in order to multiplex the tubes. For the numitrons, I intended a very similar circuit, where all the anodes of each tube are connected in parallel, and the common cathode is connected to ground when I want to display on that tube. I also considered running each Numitron on its own shift register and daisy chaining them together, but I want to wait and see how the circuit works first.