First, is absolutely great, what you are doing here,

First, is absolutely great, what you are doing here, and I would love to be as skilled in coding as you. I am learning. Maybe somebody can help me? I would like to install 2 WS2812B stripes along a 12m gangway, one on each side. On the strips I would like to simulate a blue sky with slowly moving white clouds, getting larger and smaller.(maybe could be linked with real weather data later?) I am experimenting with an UNO, but probably will need a Teensy3.1 to run it. However, how would I approach the code?1dNoise? Sinus waves controlling colorpalettes? Any hint in the right direction or sample code would be appreciated.

Depending on the density of the LEDs, a uno, or even something easy to package like a Nano or Pro Mini will be more than enough. 12m x2 x 30 is 720 LEDs -the memory of the 328P should cope with that

Either one per side, or linked across the gangway, somehow.

You can have two strips perform different patterns, but it’s not easy -might be better as its a new technology for you, to have two separate Arduino - you can get a Nano for under $3

As to the code, I’m not good enough to help with that, sorry.