I am currently working on some missions for when my group decides to let me GM (we have alternated so that everyone will get a chance to GM). So One of the guys wanted to be a Rogue Trader, but was also considering the Reaver alternate career. I have some ideas of what I could do after that happens, maybe send forces of the Holy Inquisition against him, but other then that, I don't have many ideas. What do you guys think?

The inquisition doesnt really attack pirates and reavers their more concerned with bigger threats. But the navy could certainly be chasing him.

And iniquity would probably be a better resting point for him than say footfall. Look into the back ground of the screaming vortex from the black crusade book as well.

If he had controll pf some very powerfull xenos tech or was selling halo artifacts into the imperium theat could attrack inquisitorial attention however.