I'll be flying business class on a 787, so I will be getting off the plane quickly anyway. But it will still ble a close call...

Yes, you need to go through security again because the skytrain from T4S arrives landside (at the baggage carousels).

Yes, LATAM is responsible for putting me on another flight at their expense.
But I don't know where that would be because I've added more stops than necessary (tier run/seeing several cities in a couple days). They would most likely put me on a simpler routing, for which the price I paid would have been way too high.