I would not necessarily recommend to build a modular to get a lush, dreamy type synth.
It's difficult to play polyphony on a modular. For dreamy pads stay with your Matrix.
Modulars are more awesome strange noise and slightly out of tune machines.
I recommend to start with the typical building blocks Osc/VCF/VCA/Envelope/LFO. Add a Modulation Sequencer for fun.
Add one or two mystical modules of your choice for individuality
Atlantis is a synthesizer on it's own, like your mother (no insult here).
A main component for the sound in the mylarmelodies video is the Eventide reverb box, I think.
solitud.de | YouTube | Soundcloud | Bandcamp