This ability triggers only once each turn." If the ability granted by Well Rested triggers in an untap step, it goes onto the stack at the beginning of the next step (usually the upkeep)
If a spell cast from your graveyard this way would be put into your graveyard, exile it instead
I wouldn't recommend running this in most Black decks, but the Life Swap archetype most commonly led by Selenia, Dark Angel will want to test this, as it's made to go down to dangerously low life totals and then shoot back up
The whole conversation, interestingly, started several years back when he and I talked about how threshold didn't do a great job of showing two states
Whats your favorite delirium card
Store credit here, not a fair offer there, and Ive run the gauntlet of rude shop owners