Build a Drama Frame
Start with the social arena, not a lore encyclopedia. Heartline needs a place where the same people repeatedly collide and where private choices can have public consequences. A dynasty, academy, court, small town, celebrity scene, hospital, political office, ship, theater company, magical house, or luxury hotel can all work.
Create a Drama Frame that answers: What gives people status here? What is hard to do privately? Which obligations compete with personal desire? What kinds of events force people together? Which relationship types matter besides romance?
The included Dynasty at Dusk, After Hours Academy, and One More Summer frames demonstrate the intended level. They are patterns, not mandatory settings.
Then create a small set of Locations, Groups, and recurring Events. Each Location should have social meaning: being seen on the royal balcony should not mean the same thing as speaking in a locked archive. Each Group needs an agenda and internal conflict. Each Event needs stakes beyond 'people attend.'
Do not build hundreds of files before you know what players will repeatedly choose. Start with an opening cast, three to six important locations, two or three groups, and a few event types. Add more only when play needs them.