Okay, so during my absence... here is my plan:
I am going to establish some of the setting and your surroundings and then remove Valen from the situation (it will be a casual one). And then I am going to let you guys chat in character for the week I will be gone. What I am looking for is for you all to throw around, "Hey, remember when we..." type scenarios that are of your own design. Stay with things that you guys have done as Onyx Wind, since you each have no previous Spartan experience, having been pulled directly out of training and being reassigned to this team. Obviously, avoid anything that is game-breaking and impossible (such as, "Yeah, and that time that I single-handedly wiped out the entire collective of Convenant races, that was good times!"). Keep it feasible and remember that you guys are a team (and a family, of sorts).
This 'locker room chat' should work in such a way as with one person giving a tidbit of a past mission, and leaving it open to additions... which another player will then build on, and so on. You guys will be forming cooperative story elements about your team... and will get to feel out your characters' personalities, as well as those of everyone else. And hopefully, as this is happening, you guys will get to build up your teamwork and get an idea about the pace of all of the posters involved in the game.
What are your thoughts?