1) Heavy Firepower - Does the figure that declared an attack need a red die in its attack pool in order to trigger the effect or can a figure without a red die trigger it as well?

2) Power To Shields - A little unclear about the timing window to ready the card. If you don’t pay the 1 threat to ready the card immediately after the trigger, can you still pay 1 threat during the status phase or would the card remain exhausted until the end of the mission?

Take a look at the single minded class card to see how it's different.

1) Yes - removing one red die is the cost to do the ability.

pg 8 RRG "Class Cards"

"If this cost cannot be paid, the text immediately following this cost cannot be resolved."

2) Power to Shields is worded this way because you normally can't pay threat to ready it on an opponent's turn, like Single-Minded. This allows you to ready it and potentially use it again on the opponent's turn. Single-Minded may only be readied on your turn. Both of these ready in Status phase. The benefit of readying them early is to use them multiple times.

3) See above.