I would approach the second question differently: Those are not simultaneous effects.
When a target hits 0hp and enters the destruction check, or when a dard is destroyed by a card effect (not HP) you enter the "unless otherwise stated" phase of the desrtuction check.
This is where Lady Luck, character cards flipping sides happen.
These are the "When a card would be destroyed" effects.
Next the card that is being destroyed must be dealt with, which includes its own text about when it is destroyed. It is still in play, it resolves it's effect then leaves play.
As it leaves play all other effects that occur when a card is destroyed trigger.
Bunker would not trigger tome of the unknowable. That would be wrong. An action that occurs because a card is destroyed preventing that destruction would prevent itself. Bunker can't draw a card because Tome wasn't destroyed. But then Paradox.
I'd put the order:
1: Destruction check is triggered.
2: Is card indestructible, if so stop.
3. Check for would be destroyed effects and resolve.
4. Check destruction target card for destruction effects and resolve.
5. Move card to trash, or other place if appropriate.
6. Trigger remaining "when card is destroyed" effects.
I honestly think we overuse the order of cards played rule, it doesn't work well here.
This issue reminds me of damage timing, "would be" rext can take place before damage is certain, and before a destruction is certain, while "is dealt" takes place after damage or destruction is certain. But even then there is timing differences. Legacy can reduce damage when he is dealt damage, and AZ can turn damage dealt into healing, or respond to it with Isothermic. That last example takes place after damage is dealt, not while it is being dealt. It is a response trigger. Bunker drawing a card is more AZ's Isothermic conductor timing than damage reduction reducing damage, it is a response trigger.