Laura, you hit the high points, it seems to me, in terms of plotline points. Seeing as the movie is about the struggles of trying to get a farm up and running, it's not surprise that three big events -- well, two really big ones, another which is not as dramatic visually, but just as impactful -- are tied to weather and the land:

* The tornado: Not only a danger in and of itself, but a metaphor for the "storm" within the family. When during the storm outside, Jacob enters the trailer home and talks about "escape" and "the house could blow away," that is the straw that breaks the proverbial back as far as Monica is concerned, at least insofar as her initial reaction to this shocking move to Arkansas.

* The fire: A major reversal, indeed, the destruction of what Jacob had worked so hard to build, the barn a symbol of what the farm *could* be. And again, the event in the plotline spurs trouble within the family as Soonja disappears, a crisis the family has to deal with.

* The water stops: You can't have a farm w/o access to water, so while this may not be as dramatic visually, it certainly up the stakes and odds against the family's success with the farm.

I think you are right that the David - Soonja relationship is the central one in the story, however Jacob and Monica is also a powerful subplot. It's interesting to track both of them, how they compare and contrast. But we can discuss that further in Part 3: Characters.

Overall, this is very simple plot. Which brings to mind something I coined a while ago: Simple plot. Complex characters. I think that works for "Minari."