If you really want to go anywhere I'd suggest you starting small. Like make just one neighbourhood. It could first focus on how those people try to make that particular block safe for themselves. This should give you enough time to plan on elaborating the story.
While I did not play in the beginning of this version of Bluzone, but what I gathered was basically the following: there is a small group of people (who know and care about each other) exploring an unknown area. Maybe that would work the best for a start.
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