Thread: First Ambient Rack
You'd be wise to listen to Lugia's advice.
Marbles is a natural for what you described, but also check out Bloom if you want deliberate direction to your generated sequences. Warning: Bloom is a love it or hate it module. Read the reviews
Zadar is amazing and can add slowly evolving complex modulation to your ambient soundscapes
Everyone needs Maths or another DUSG
Effects to check out:
FX aid is a favorite for traditional effects.
Make Noise Morphagene, Mimeophone for creative effects
Qu-Bit Nebulae
Instruo arbhar or Lúbadh