Hey.
I might be running Hell's Rebels pretty soon, and I was thinking of an introductory, prologue scenario set before Barzillai's occupation of the city where the PCs can meet, work together, and get a good tour of Kintargo and it's major locations.
I was thinking the enemies could be urban criminal gangs, assorted monsters, or low-grade Thrune loyalists. However, this would be before the Citizen's Group is fomed and Barzillai is in power, so I'm not sure what kind of a presence they would have.
What do you think?
I would suggest getting their character creation and backgrounds underway as soon as you can. Once you have that information, you'll probably be able to create a more organic introductory scene that puts them all in touch with one another for sensible reasons.
As an example, I am going to award my players a Craft or Profession skill as a class skill as a custom trait to encourage them to use that to tie themselves to the community, as well as design one particular NPC for my use that is important to them in some capacity. To make the fact that Kintargo is home not just for soft and fluffy reasons but because it is where they have made their livelihoods and where they have people they depend on/who depend on them/whom they like/who are rivals, etc. If I get all or most of them to bite, then depending upon what professions and "day jobs" and such they have, along with their contacts, I can weave a launching point like you suggest that will lead to the inciting incident outside the Opera House.
If you want to throw some low grade bad guys at them, I might suggest using these early encounters to introduce some of the NPCs they will come across later. Like maybe that dwarf holding hostages in the salt mill, or a pack of Thrune loyalist thugs who later join the ranks of the Chelish Citizen's Group and suddenly have a few more "resources" they can use to be antagonistic towards the PCs who gave them a rough time.