Thanks Semtex9 for your extensive, meaningful and very technical reply. I am a programmer with hardly any knowledge of electronics. To clearify my 'situation' I have enclosed an image with a part of my scheme.
Thanks to another subscriber of this forum I have managed to delegate the code for the Landinglights and the Deflector Disk to two ATTtiny85's. They don't need extra current to work properly, so that's fine. I also knew to use a L7805 positive power regulator to make a 12 Volt adapter run my 5 Volt Atmega328P.
Now I would like to resolve the issue of giving current to a group of LEDs, controlled by a single port on my Atmega328P. During the build I glued all the 80 LEDs in the model with each having their own resistor. So I can plug in a 12 Volt adapter to light the model, which looks nice but I want to control the lights. According to their function I have made 7 bundles of grouped LEDs, so practically I have 7 different coloured wires sticking out the front, each of them serving multiple LEDs. As an example: for the main lighting I have put in 30 warm white LEDs with a total of 600mA. From here I'm lost.... I don't know how to solder this on a PCB-board with which components 
.
Can somebody help me?
Kind regards,
Jan Speyer
The Netherlands
