Aaron's motivation for intervening at the party is to get money from Granger.My father came up with this. Aaron is shown in the film as being selfish and willing to do anything to get ahead—he even cheats at Scrabble. He doesn't want so much to actually save Rachel as he does to look the hero in order to impress Granger and get some VC funds from him.
The time travel box kills the person who uses it, replacing them with a Clone.This has been kind of/sort of confirmed. Clone Degeneration does effect Abe and Aaron according to the Word of God. But it could be assumed that their souls or consciousness was transferred to the new body. At least that's perhaps what Abe and Aaron are telling themselves. What might really be happening is that when Abe and Aaron have those moments in the box when they feel content or start to have visions, that's when their original selves are dying and their dopplegangers are spontaneously coming into being. If an afterlife exists in the movie's universe, then the final versions of Abe and Aaron (when they finally die) will find themselves sharing it with dozens of "clones", some of whom were only alive for a few hours or days.