I think so too. Almost a flashback, describing what they were doing the day that they were taken. I think that would shed some light on who they are. When you've been abducted by aliens, and you're trying to escape, you probably won't be acting like yourself right away!

I think physical creatures would be easier, yeah, in case we want to incorporate some character/alien combat. I think we could definitely run with the caste system idea. We could have different tiers of alien life. They all belong to the same race, but they have different forms and abilities. I'm sort of thinking Halo Covenant for this. There could be the mindless attack-dog pawns that are just soldiers. They could be controlled by some sort of troop leader, who controls them through the hive-mind. The troop leader answers to someone above them, who perhaps has more advanced psychic abilities. Their intelligence, and abilities grow with their higher ranks. Maybe those above the plain pawns can have their own personalities/character? A race-wide hive-mind might not be as fun as finding different aliens with varying abilities who can think for themselves. 

And CS's would be great! A number of my 1x1 partners have preferred to jump right in, but I find making a CS helps me collect my own thoughts.