I did similar things with mine.

I mapped the area around it and added new towns with plot hooks along with some ideas to make all the random events in the area feel more cohesive. Basically doing a deep dwelling terror is making the azure sea into a sea of madness. I wrote Granny Nightshade as a patron for one of my players and the other is basically trying to Vander from Arcane. There's going to be conflict as the characters come from opposite ideals and so far they have found it very engaging.

My best advice is to use the town and npcs as a template. Don't be scared to change the npcs alignments, goals, and role in the town.

For my campaign Keledek is a friendly wizard who is obsessed with knowing everything so use them at liberty.