Making a movie is hard but all good movies can be told in one two sentence the trailer you guys put together is a good reference for that. Even though this movie will be based on the game engine I suggest you try to draw a story board and if it will be with speaking (instead of typing) then you will need to make an animatics for the purpose of marking the time for the dialogs and see how long the whole thing would last. Animatics would help even if you decide to use typing for the dialogs.
Anyway I wish you guys good luck.
