While not staff, I have NPC-ed for EOS a number of times, I can answer the majority of those.
1) No cost if you preregister.
2) Like most larps starts Friday evening-ish (9-10 or so... Ken?)
3) Yes. Yes you may.
4) NPCs stay in CC (Monster Camp), the main building right in front of the parking lot, there is in fact a room full of bunks
5) No "official" game off, but it tends to quiet down in the wee hours of the morning, generally as long as people are willing/active stuff happens (short answer bring on the energy drinks)