So the LED boards came in yesterday and my bad luck with ordered pcbs seem to continue - the footprint of the RGB LED is to small! I guess that is somewhat the mistake of the user who made the part and the crux of 123d.circuits.io - nobody checks your work. Carefully drilling the holes bigger could work, but my drill bits are all broken and I have to wait for the 150Ohm smd resistors.
Since the atmega328 current per pin is about 40mA I think I will drop the ULN2803 for now and focus on the main board with the linear potentiometer and the led display and finally get a decent case and the power setup done.
I also started a nice little distraction - LED nixie tubes http://hackaday.io/page/436