Maybe a dumb question, but why does the cosmology matter? How does it impact your game at the table, at least at the beginning - and even later? As noted in the quote from the DMG24 above, the way to get to various planes is through gates or floating on the Astral Sea. The "spatial" relationship on a 2D map is just for human comprehension.
I do agree and like the idea though of Chaos trying to break down Order; but then again, I always was a fan of the 2nd law of thermodynamics. (Irony alert! It's the 2nd LAW, the LAW OF ENTROPY

. It's got all the Chaos folx really pissed off tbh)