Pitching ET

"A Boys Life" is a story about the relationship with two outsiders. The one outsider boy by the name of "Elliot" that felt like he could never fit in, finds himself encountering something that would never fit in with his world as well by the name of "ET". The story provides a series of events on the relationship between the young boy and his alien, and the trials of tribulations they deal with in between.
Our main protagonist Elliot comes across this alien after he is left behind from his family. Outsiders that try to capture them disrupt the landing that his UFO lands on, and their mission. ET is the only one that does not make it to the ship and is sadly left behind with nowhere to go. He some how gets to the backyard of Elliot in which they run into each other and begins our story.
The story progresses with the missions Elliot goes through from hiding the alien from his mother, making sure that his siblings do not tell anyone about him, and ultimately saving each others lives. By the middle of the story, we see how Elliot and ET become to in sync with each other, that they ultimately share the same feelings and experiences. It is as if ET is living through Elliot in the world that he does not recognize.
While this is all going on, ET becomes sick in this new world, which ultimately makes Elliot sick as well. With their struggle to survive, and Elliot's mission to get ET back home, we are set with another journey of escape. Elliot finally gets ET to his departure point after he resurrects from the grave, and is picked up safely back home; but their friendship seems to never end.

Questions:

When thinking about pitching this movie, who would you include in your cast as being the most important and why?

When pitching this movie, what sort of details would you include? And also what details do you feel aren't worth discussing?