I think the question you're asking is where to store the data for the LEDS - and that depends on where the data going to come from. How is the LED sequence going to be defined? With that many LEDs it would hardly be practical to define every transition manually and perhaps you're going to generate them from some sort of rendering application. Is that going to be done on the Arduino, or done in advance and with the output made available to the Arduino in some form? You need to know what sort of formats the data will be available in, and how much data there will be. Given that the number of LEDs, even a single state is going to require 1800 bytes of data and that will increase substantially if the display is going to change. You might want to store the data on an SD card and have the Arduino read it as requires, or store it on a PC and send it in real time over the serial port. If your Arduino has a wireless or network interface, you could send it over either of those, too.
As I understand it these LEDs are programmed by shifting the display states out over a serial data bus. With a very large number of LEDs, the propagation time for all that shifting would restrict your update frequency and might become a problem. In that case you could divide the LEDs up into several shorter strands to make them easier to manage. But that would only be required if you have performance issues.