You'll only be able to do six talks/events with other characters. Note that you can only trigger the events for Rem, Sice and Trey in the VIP Suite when you're first there, as the events will not be there upon leaving and re-entering.
There are also a couple of tasks available though they cannot be completed on a first playthrough. Explore the city as much as you can before opting to do quests so you can see which ones you can complete.
|District 0709||Imperial Trooper||Ether|
|District 0709 (by exit to District 0711)||Imperial Trooper||Hi-Potion|
|District 0711||Imperial Trooper||Ether|
|District 0714||Imperial Trooper||Hi-Potion|