First BIG Campaign

I'm doing my first large scale campaign. Full world building and everything done by me. But I'm having trouble thinking of how to start it. One idea I've had is starting off with the party dead in some way and make their first major quest regaining their bodies and figuring out what happened to them, who or what killed them. I'm just stuck trying to figure out a good way to do that, maybe even check out or make some homebrew subclasses that would work well whatever I can come up with for how they start.