The more I think about it, the more I realize that this is not about the electronics, but about the design and realization, which I will never be able to accomplish with my skills (and tools). Somehow similar to the QlockTwo idea. Back to electronics: I think one can also daisychain 8-bit shift registers, one for every 2 RGB LEDs, for a total of 30 pieces, no PWM though, if that is indeed needed.