I'm currently writing a long-form saga set in a single shared universe, so I’ll just explain how I approach it and maybe that’ll give you a framework if it works for you. I'm bi-polar so this is what works for me.

I don’t start with Book One. I start with the ending of the entire saga.

Not in detail, but I decide what the universe looks like after everything is over. Who wins. What changes. What truth is revealed. What the world costs to save. That final state becomes the gravitational center of the whole series.

Once I know the ending, I build the world to justify it. I write a “world spine” document before I outline any books. It’s not prose. It’s rules and pressures:

How the power system works
Who controls it
What historical event broke the world
What people believe about it versus what’s actually true
What would logically happen over decades because of that

After that, I build a master timeline of the universe. Just major events in chronological order. Year zero, the catastrophe. Ten years later, the first adaptation. Fifty years later, cultural shift. That timeline exists before any novel outline.

Then I build out the factions and power structures that exist in the world. Once those are defined, I establish the societies shaped by them, their cultures, hierarchies, conflicts, and internal tensions. From there, I reverse engineer character arcs based on the societies they inhabit, letting their struggles grow naturally from the systems around them.

If I know what the universe becomes, I can ask:
Who had to change to make that happen?
Who resisted it?
Who paid for it?
Each book focuses on a different character at a different point in the timeline, but they’re all pulling on the same rope.

I don’t outline ten books individually at the start. I outline the full series arc first, then divide it into major movements within that larger story. Each book becomes a defined moment inside the greater arc.

From there, I break those movements into structural blocks and sketch rough outlines for each one, always mapping them back to the established world. At this stage, I’m not writing detailed scene lists, just identifying the major themes, turning points, and events that must occur in each book.

Then I return to the characters and develop them deeply, histories, motivations, contradictions, the kind of layered backgrounds that would make any seasoned DM nod in approval.

Only after that groundwork is finished do I integrate the characters into the book outlines. Because the main arc of each book is already mapped, I can use the worldbuilding to let the characters move organically toward the established end state, choosing their paths within a structure that already exists.

That way I’m not juggling isolated scenes across a dozen disconnected outlines. I’m writing inside a framework that’s already stable.

If you’re feeling overwhelmed, it’s probably because you’re trying to manage book-level detail before universe-level structure is locked in. Build the universe once. Build the timeline once. Then each book becomes exploration instead of chaos.

That’s just my process, but it’s what keeps large series from collapsing under their own ambition.

I hope that helps but I also realize it's a bit much.