How many universes "branch off" from a "quantum event", and in how many of them is the cat dead vs alive, and what about non-50/50 scenarios, and please answer so that a physics dummy can maybe kind of understand?

(Is it just 1 with the live cat and 1 with the dead one?)

Although this gives the correct answer as far as the number of worlds is concerned, it sounds strange within the MWI (which was supposedly assumed in the original question).

I think you can't do MWI justice without introducing the observer in the game: apart from the coin which lives in a two-dimensional universe, there is the observer whose mental state lives in a (at least) three-dimensional universe. The dimensions of the observer's mind are "think the coin ... (read more)