Chain of Acheron

I’m going to be DMing a game where my players are junior ranked officers (lvl 3) about two years after the event in black bottom. I’m Setting up the campaign to have to players fight a different black iron pact, then eventually a lord who follows the teachings of Ajax. But having issues putting that idea down on paper (probably just writers block). Getting it started is the part I’m struggling with. I decided to do a slow burn type of game. Has any one else ran a game like this and how did you begin your game?