Er, use actual names, because for a second I had no idea.

1) Maybe? She falls into the "not actually part of Gensokyo and has never been seen IN Gensokyo" camp.
2) No. If anything, Eiki would probably be [i]her[/i] boss. Nor are the onis actually... in hell. Neither is the Palace of Earth Spirits, so... random offhand comments are unimportant. <_<
3) Yup. Except where you can have them stuck in the recent past.
4) Please stop asking so many questions.