Hm I was under the impression the entire point of Quantum Entanglement was that observing one entangled particle caused the other to change as if you had observed it, which would imply a change of state causing another change of state.

The additional three dimensions in the Material Plane are mostly the same as the first three- essentially, at each point along any of the additional three you'll find a layout of stars and galaxies similar to its neighbors but slightly larger or smaller as one moves farther or closer to the 'edges' of the plane. The final three dimensions of Yggdrasil are the ones more used in the phasing and shadow-walking examples you mentioned, as the first six are folded through them.

The chemical and physical effects on the mind don't directly change the core personality, I think. The experiences caused by living with those changes can, just as normal life experiences change a person's personality. In that sense, yes, the soul and brain do influence each other- I'm not sure what you mean about Depression being a physical illness rather than mental, it's already known to have chemical aspects due to hormonal imbalances, whether that is a cause or an effect; I don't know quite enough about psychology or neuropsychology to make a universal statement, but I think (at least in this system, if nothing else) most quantifiable disorders are at least mostly in the brain or mind rather than the Core Personality aspect of the soul; some may be reflected in the Core, especially if it's something that that person considers part of their Identity, but mostly they are layered onto the Core by malfunctions in the brain and its ability to properly express the Core personality.

Thank you for taking an interest, though!