Oh man, I used to love that movie. The popcorn, man...
*ahem* Anyway.
Benji is...well...basically an almost-self-insert wearing Johnny Gallagher's face. I should be ashamed of this, but I'm not. So there. (Though judging from his Twitter, Benj might also be an almost-JGals insert too...not ashamed of that either.)
Ethan doesn't really have an inspiration either, unless you count the fact that I wanted to play an arrogant musical theater geek and look at Skylar Astin.
I wish my explanations were more...useful or impressive or something.