If they have any sense they'll focus on the Inquisition or the Imperial Guard (who after rounding to like 12sf are responsible for about 100% of the Imperium's fighting ability*). Start with the human characters, and slowly transition the focus to the borderline heretical mutant scum gods among men as the series goes on.

I'm not holding out much hope, but maybe like Inquisitor: Martyr I'll be pleasantly surprised. Maybe this time they'll remember to add the middle aged woman in power armour in at the start of the series.

* When you run the numbers Space Marines make so little impact that recruiting them from any major Guard world is the worst thing you can do.