yer that would work well as an ODST vest because of the straps and ease to put the armor onto it
I dono about using a jacket, you might aswell just attach the armor to a BDU black shirt.
I reakon that in the WETA they use a Black BDU shirt and pants, because it looks kinda loose. A flight suit would be ok but i think that its better to go with separate shirt and pants because you can get betters fits there easier to find and from my experience of using a flight suit as the base...