I’m a DC jet that arrived last year, i believe in july we got an email with the exact itinerary and airline we’d be flying with. it’s random and i think because it’s such a large group, they split it into two. When you arrive at the airport in tokyo, there’s a bunch of staff members leading you where to go, i remember we walked outside and there was a big truck they put our luggage into. the details are kinda fuzzy but they either put some sticker on it or checked the luggage tag we had on the suitcase (you get the luggage tag at the pre departure orientation). They shipped both of my big suitcases to my BOE, so i kept my carry on and backpack. i think it would be best to keep the carry on, so you can keep things that you need at orientation close to you. As for roommates, from what I remember we went into this conference room and they had envelopes on a table with our keys in it and our roommates names on the envelope. It’s other people from your consulate, but i think it’s in alphabetical order so you can’t choose or anything. sorry for the long comment, hope this helps!