In regards to Wounds reducing a PC's Grit, is that a death spiral? Does the PC use the lowered Grit value when making a Grit roll from that point onward? Or is the player just tracking the wounds, effectively making a PC have 2 times their starting grit in HP?
I would say it is kind of a death spiral. The hit points reflect more of the superficial physical damage and exhaustion. Once you start taking damage to your grit, these are more serious wounds. And yes, that means that when rolling grit, you are rolling against whatever the current value is, even if that has been lowered by wounds.