Hi there! First off my name is Brian and I've been a Gamemaster for a few years now. I'd like to think I have gotten quite good at it but I'm running into some issues and questions that I'm having issues answering. 40K is a favorite of mine as I play Tyranids in the tabletop and have played every FF RPG in the setting. Typically we end up running Rogue Trader or Deathwatch, but my group has been on a 'evil campaign' spree and wanted to go for Black Crusade. For this particular session I only have two players who decided during character creation to be close friends and followers of Tzeentch, so that they could scheme together and not against each other. My idea was I wanted them to conquer this planet then slowly spread out, gaining more infamy as they conquer until they can finally start a real Black Crusade. I started them off with a ton more XP than normal just because this is meant to be casual and we've never experienced high level Black Crusade play (Usually the games fall apart before then.)
My main problem is finding fun ways to challenge them when taking this planet. As servants of Tzeentch they obviously didn't barge down the nearest door and start blasting people, instead opting for looking around the city they arrived in and assessing the situation. For this to make sense I have to explain the planet a little bit: The planet is owned by a Rogue Trader by the name of Lord Tidus. The planet has very little farmable soil but a lot of valuable minerals and thus it is primarily an industrial planet which manufactures arms, armor, and other misc goods. The players decided the best way to start was by disrupting the manufactorum in the port city and convincing the workers (Who obviously are underpaid and under threat of death should they try to leave) to side with them, using deception and other methods to slowly convert them to Tzeentch along the way.
I really just need suggestions and ideas on how to properly challenge them with the idea of conquering a planet. What would be good points of interest for the players to take over? What kind of conflict would be fun to encounter when doing this?