First, welcome to CruiseMates and cruising in general.
1. Depends who is on spring break, and then again how many people are willing to go. 3 day cruises are good because a lot more people are willing to miss school/work/etc... I honestly have never been on a cruise THAT short that is actually in memory, so I can't judge for you. There are always teens - whether it will be a raging party, it is hard to say.
2. It happens. The game just changes on the shortened cruises because of the limited time to get to know people. Think of it as a one night stand as opposed to a weeklong relationship.
3. I, nor anyone else on this board, can answer this question publicly (privately I have no control over). All I can say is use common sense.