I can't see Advisors being host bodies really, I mean, didn't one of the Vorts in EP2 mention something about the Advisors who've begun to "hatch"? - For me at least, it sort of removed the impression that Advisors are used as host bodies and the theory of Breen being one.
As far as i know it was planted there, or fell from the sky or something, it's crate is pretty deep apart from those big pillar things bombarding the ground to keep the ant lions away
I've been playing through episode 2 a few times and i'm always as dissapointed as i was the first time during the final sequence with the striders and hunters(those who've played it through know what im refering to)
And i've been making up for it by npc_creating some combine soldiers and now...
no, because the citadel in City 17 was the main citadel of Earth, hence why Dr.Breen had his administration there, once the citadel in C17 was destroyed, the others in earth went offline, aka they're not working at all