When I start Halo games I usually start out on Heroic, then I go into Legendary for my second playthrough. I beat ODST on Heroic, had a blast, and now I'm going back to beat it on Legendary. But this game is structured differently than other Halo games... whereas, you can actually launch missions from the "Mombasa Streets" mission by going to each beacon.  
 
So I'm wondering, how can I complete this? Can I just play each individual level (where you play as the different soldiers) and then Data Hive and Coastal Highway, or do I have to actually go through the city and launhh each mission from the beacons in order to get the credit for Mombasa Streets, since it's not really beatable level when you select it from the mission replay?