Disclaimer: I am posting this for 3 reasons. 1. I'm bored. 2. I've been drinking. 3. I'm lazy and figured putting my existing ideas out there may get some ideas in return.
This is how I'm running my, I don't care about power-creep balls to the wall, open world Ascension game:
The group (Inquisitor, Vindicare Assassin, Templar Calix Interrogater, Magos, and Stormtrooper) ran through the Ascension book pre-made, Red Wake, with little trouble. By little trouble I mean the Inquisitor had to shoot the now Magos' previous character (Desperado) for heresy. It happens. After that I told them it's entirely up to them where to go and what to do.
So, this is what I do. I came up with roughly 10 one to three session story arcs and have seeded them throughout the campaign (which means whenever I remember them). A NPC will bring up something that is happening on another planet, the Inquisitor's lone Acolyte group will dig up something he will deem is appropriate for him to handle, or some other Inquisitor/Adepta member/old friend/etc will go to him for help. It is up to the group to decide what to investigate, what to dump off to the Acolytes to handle, or what to ignore. These story arcs may or may not have timers and may or may not have significant impact on the Calixis sector itself. (I should probably say that my group consists of players that have been playing RPGS together forever and work together well). The power-creep problem I have, sort of, solved by the players own horrible "insight" and the judicious use of horde rules. They can carry around all the armor and weapons they can requisition but when they go on to certain planets or go undercover they only have what they can bring. Sometimes they plan accordingly.... and sometimes they burn fate points.
Here's where the lazy part comes in... I'll lay out my story arc ideas in the next post for people to steal and say they came up with them because they are incredible and then you can give me yours which I will steal and say they were mine because they are hopefully incredible. We all come away with bigger egos and lots of win.
TL:DR - srsly read it. You already clicked on the post.