To get to level 2 before touching the transponder, you've got to do everything, as well as killing everything; certain actions on the ship grant small amounts of XP. Exploring every chamber, even the one you don't need to go into, pushing the button there and watching the cutscene, etc., You've also got to kill all the little things that only give one xp each, such as the injured thralls, even the ones who are green to you.
Other than for experimentation, it's not really worth the time and effort it takes, but it's still an interesting exercise.
A safer (and more boring) way to do this is just to make sure that your entire party are up top on one of the raised areas by the time the cambions show up, and hide. Then you can just take your shots/spells, and hide again every round, and they'll never see you, and so will just stand around and growl at the air while you whittle them down.
In terms of who can throw what, it's all based on strength - Creatures have a weight, and characters can throw things under a weight threshold based on strength. A nifty extension of this is that characters with 12 strength or more can throw 40lb, which means they can throw halfling team mates around.
