Hi,
Big project.
The most important is to know about the currents.
3000 x 1.5W = 4500W.
4500W from 12W = 375A.
I doubt you want to use (find) a single powersupply that delivers 375A.
Thus you need several power supplies.
I don't recommend to connect several switch mode power supplies to get one big supply.
If you follow this recommendation, then (now) you have several channels, each with one or multiple controllers.
--> decide which power supply you want to choose. Then go the next step.
*****
Multiplexing:
* if you want (almost) full 1.5W brightness: then the current needs to be multiplied (indeed mathematically divided) by the multiplexing rate (a bit lower not to overdive the LED. --> Read the LED datasheet about SOA when multiplexing).
DC current for a single LED is 1.5W/ 12V = 0.125A. With a multiplexing rate of 1/8 = 0.125 --> the "ON time LED current" should be close to: 0.125A / 0.1245 = 1A
I recommend no to drive them beyond 0.9A. --> read datasheet.
* if you don't need full brightness, then you may use lower power LEDs.
--> re calculate the overall power
****
You need careful wiring. Usual LEDs brightness is very critical with voltage. If you reduce voltage by 10% it's possible that the brightness goes down to zero.
--> read LED datasheet about V-brightness behaviour. Usually a LED brightness is very linear to LED (average) current.
Thus you may consider to use "current control" for the LEDs to get equal brightness, or you need to add series resistors (calculate power dissipation) to ensure almost equal brightness.
All the wiring creates voltage drop. This may harm (equal) brightness. Thus the decision above also influences wire gauge.
--> Calculate wire gauge not only about thermal considerations, but also on brightness (voltage drop) considerations.
****
As in the video there are several LED strings. Decide if you want to control each of your 3000 LEDs individually - or you are able to create groups of LEDs where only the "group" has to be controlled. (Makes LED control more simple)
****
Consider overall power dissipation of the controllers and the LED drivers. This may be a huge amount of heat. You may need a huge box, heatsinks, fans...)
Klaus