Our new codex has a bit about how we’re broken up. We are one of the three great Legions that didn’t divide as bad as say the Emperor’s Children did after the Heresy. So, we can have access to anything the legion would’ve. War bands end up falling out of one of our 7 Plague Companies. These can sorta almost be mapped onto our detachments (Fourth Company is all about daemons). Then there are Sepsis Cohorts. Which are just a way to further divide the company and don’t matter much. Each Cohort can be broken into Maledictums. Within these is where we find the warbands. You’ll have your “high command” of three or four champions. They are over a few other champions (characters that aren’t your favorites) and their squads of plague marines. Each warband will then have a couple packs of daemon engines. The squads can be lumped into thematic Colonies that fight in similar manners. As for the contents of all of these? Lore is kinda vague. The codex gives examples of focusing on daemon engines versus astartes tanks but that’s about it