10 – When an enemy attacks me, can I exhaust an ally to defend and then also play the preemptive strike…

Yes. We have added a ruling to the latest Rules Reference update under “Defend, Defense” specifying that Defense-labeled abilities can be played during an attack by a player whose ally is defending that attack, in which case, the player’s identity does not become the defender. (Only one character can be the defender of an attack at a time.)