I should clarify that my intention with the two suggestions I made was an either or, not both together.
In other words, if you're not fully prepared with a huge amount of material already written out and available to the players, then run it as a points of light and fill in details for the players as their PC's discover them.
In other words, if you're not fully prepared with a huge amount of material already written out and available to the players, then run it as a points of light and fill in details for the players as their PC's discover them.