followup on question #2:
It appears that sea vessels can choose to engage the Sub, but it can just submerge and immediately disengage at the defender’s option (unless there’s a destroyer present, natch).
That would mean that the attacker was denied both an opportunity on the sub, but since they attempted to initiate a sea battle they also couldn’t do a bombardment. Right? So if you want a guaranteed chance on a sub, you need to have a destroyer accompany. Or ignore the sub altogether, and suffer their attacks next round-which would be brutal, because a sunk defender couldn’t respond.