Forbidden Lore (xenos) will set you back 500xp, because of all your personal xeno encounters.<br/><br/>It's perfectly fair to assume you can get your sanctioning, yes, if you're buying it outright.  You'll likely need to work harder to convince the Kroot to join you for shaper status, though.<br/><br/>As for the Tau rail rifle, in Rogue Trader, I would give it the accurate quality, since Devastating doesn't have any meaning in the rules of Rogue Trader.  Its main function is to be a light artillery piece that you use like a sniper rifle, though.