Hi Paul,
once again thank you for your input! 
Paul__B:
I can't see the point in using "delayMicroseconds()"; I would at least use "delay(10) " at each step for testing purposes.
At my first trials, I used the "delay()" function but recognized, that i needed a more detailed timing, because with a lot LEDs switched on they started to flicker and get dim @ delay(1);. So I discovered the "delayMicroseconds()" function. With this function I could implement a delay below 1ms. But it didn't help either. 
Paul__B:
I gather you have by now, removed any reference to OE in the "loop" code, and that there is no extra delay function at the end of the loop that you have not illustrated.
Done! Thanks this was a good advice. Now I could adress the LEDs more stable. But still flickering and dim
But your code didn't work. All LEDs are dark. I still have to investigate why. I'm writing some feedback tomorrow....need some sleep now.... 