

This was mentioned (not fully, but enough to get some of the ideas) recently in an episode of PBS Space Time
As far as MWI itself, my understanding is that it comes from simply taking the same math that works for atoms (as you say) and applying it to everything - the observers of a quantum system, the earth, the whole universe. I think it really comes down to the question: If Everything is a wave function, what would it look like from the inside? And MWI pops out of trying to answer that.
And the other interpretations of quantum mechanics don’t even seem better to me, requiring arbitrary conditions for a state to collapse to a single value for example. That feels to me like an entity of the type Occam meant.
Arachnophobia
It doesn’t actually still haunt me (I’m the family spider hunter) but I did get nightmares for a while from that one.