Here are some unrelated questions that came up while playing today...

1) Once Destiny has "predicted" who will stun, there's NOTHING you can do about it once the effect has fed through the queue, right? You can't negate a payment effect later becaase it's no longer an effect. You can't stun or KO Destiny to prevent her prediction. Right?

2) MUST the defender choose to stun one of his attackers? With a solo attacker, it looks like you have to, but with team attackers, you could choose to "stun" one of the attackers who has a high DEF so that you don't actually stun anyone. Is this right?

3) This last one tends a bit more towards startegy than a rules question, but I'm wondering about good ones to deal with Sentinel Swarms. I know about Flame Trap, but is there anything else that could help a lot?

1) Once Destiny has "predicted" who will stun, there's NOTHING you can do about it once the effect has fed through the queue, right? You can't negate a payment effect later becaase it's no longer an effect. You can't stun or KO Destiny to prevent her prediction. Right?

Once the effect is resolved, there is nothing that can be done to negate it later on. Even if you remove destiny, since the effect is independent of the source, it will not help from preventing the extra endurance loss.

2) MUST the defender choose to stun one of his attackers? With a solo attacker, it looks like you have to, but with team attackers, you could choose to "stun" one of the attackers who has a high DEF so that you don't actually stun anyone. Is this right?

If you choose to stun the attacker who has a higher defense than your atk, the attacker will not stun and you will not stun anyone in the team attack. It is not required that you stun anyone (even if your attack is higher than the defense of one of the team attackers), however, it does force you to choose to attempt to stun a character before the attack will resolve.

3) This last one tends a bit more towards startegy than a rules question, but I'm wondering about good ones to deal with Sentinel Swarms. I know about Flame Trap, but is there anything else that could help a lot?

Total Anarchy + Flame Trap. Firestar + Total Anarchy. Doom: DG + Reign of Terror. My personal Favorite, turn 6 boosted Scarecrow. Those are usually considered the best options for dealing with Swarm Sentinels.

For clarity, the defending player doesn't choose a character to stun. He chooses "against which attacking character the defender will evaluate its ATK." (602.4c)

The defending player is required to choose one attacker, as was said, but it may help to understand what you're actually choosing.

For the Sentinels, how effective is Tower of Babel? Many of the effects in a Sentinel deck target Sentinels, but is stripping away the team affiliation enough to disrupt that or do they still get to use the effects because the name of their card/character is some variety of Sentinel anyway?

A Sentinel Character will not be a Sentinel after Tower of Babel is played. It doesn't matter what the name of the card is. If the card was worded "a character with Sentinel in it's name," then that would be a different story.