6 – I saw it was previously ruled that if Nova removes the last threat from The Search for Spiral via its…

No; if Nova used the ability on The Search for Spiral to remove the last threat, he would not get the ready+draw 1 bonus from Unleash Nova Force. Same for if he removed threat from Tooth and Nail via Tooth and Nail’s ability, or if his player removed threat from Spatial Positioning via its ability. Encounter cards are not considered an extension of the player’s identity, so their abilities that remove threat are not considered performed by the identity and do not combo with Unleash Nova Force. Similarly, if a player uses the ability on Common Criminal to deal damage to it, they would not place a counter on Hall of Heroes.