Hi, I'm at Camp Humphreys now and will be starting work this Monday. There does not seem to be a lot of GS positions open at this time, unless you have a degree in Engineering. The rumor is that once Yongsan starts transferring its operations and stuff down to Humphreys, there will be a lot more jobs opening up. But that transition may not happen for another handful of years.
As far as spousal preference, I am not sure you get it if you are not in the federal system already. Plus, you will DEFINITELY NOT get it if you are non-command sponsored. On the flip side, however, you may get family preference, which has less of a priority than spouse preference... but, hey, it's better than nothing!
And YES, you may definitely start applying before you arrive. Just make sure that you put somewhere on your resume that you will be going to Camp Humphreys (an exact date would be incredibly helpful). I started applying Jan 2007; we arrived here Feb 7, 2008. I got picked up for a GS job and will be starting tomorrow. But I'm apparently not the norm; a lot of people have been telling me I've been really lucky. We'll see.
You should be able to look up the Civilian Personnel office if you google the Camp Humphreys website. I actually called ahead to see what I needed to do before we arrived to Humphreys. You can do the same.
Let me know if you have any other questions! Hope this helped!
