I did decide to use just 128 RGB LEDs in a 8*16 Matrix. This reduces the the circuit to drive them. I think I will use one 16Bit shift register (MBI5026 or compatible) for each color and multiplex over the lines. The current for each color can than bes set independent.
For controlling everything there is as Atmega xx8 on the PCB. I think I will use a ATmega328p, because they can run at 20MHz and I do have some left. This panel does fit in 5*5cm so PCB manufacturing is cheap. The two PCBs wil be stacked on each other.
I will update details and description of this project to this revison. I think this will be near the final one. At least I am not planing to change the number of LEDs.