@ jkason : Nice. I can work with that.
What force? There's Planetary defence force, which means you are a local, which ranges from volunteers training one weekend a month when it's good weather so they can have a nice walk, shlot some guns and have a good BBQ with some nice cold beers with the mates to underhive gangers forced into joining to elite noble huntsmen to anything inbetween. They take care of local defence in case of attack.
Then there's the Imperial Guard which are a tithe which is payed to the empire. They range from elite units like the catachan jungle fighters, like McClane, to elite units from high-tech worlds to WWII styled platoons to scottisch kiltwearing clansman who are trained with a lasrifle but still rather use their twohanders or a chainsaw version of it. They are sent to the various wars waging around the empire, used mainly as cannon fodder, with
gaunt's ghosts as the notable exception. The series are very violent, a bit over the top at times. Nothing wrong with that imho.
Take your pick
For one reason or another, there's quite a few inquisitors in the various fiction of Wh40K that are psykers. There's the
Eisenhorn trilogy from Dan Abnett that I can really recommend if you wanna read something about the big and dark place that is Dark Heresy.
In the long term it's really better to spend your XP on advancing your willpower rather than on buying minor powers, as you get enough of them for free when you level up. And you really want a high willpower when you're a psyker.