Playing a flying race (the only one in the group) and still low level (10hp/13AC), we seem to be encountering many creatures with longbows. I was thinking about somehow getting the feather fall spell (multi-classing/magic item/other party member to take it) but wanted to know/confirm how it worked in specific situations.
Flying at 600 ft., get hit with arrows, as a reaction cast feather fall, then take enough damage to fall unconscious.
Can I cast feather fall after I know the damage of the hits, or must I cast it once I know I've been hit? I assume that since the spell does not require concentration, it will last the duration (1 minute) and I can land after 10 rounds (descending 60 ft. per round) without taking any additional fall damage (albeit prone).
Flying at 60 ft. (feather fall spell range) over a friendly caster, get hit with arrows with enough damage to fall unconscious, friendly caster uses his reaction to cast feather fall on me.
Will I reach the ground next turn prone but without additional fall damage?
Flying at 120 ft. (out of a friendly caster's 60-foot feather fall range), get hit with something and fall unconscious.
When do I actually start to fall and how fast? On the turn I was hit by the enemy, or the start of my turn? What I'm wondering here is how much time there is (if any) for the cleric to cast a ranged healing spell before I hit the ground, or whether someone on the ground can cast feather fall on me once I fall within 60 ft. above them.
If possible in the answers please include citations.