Thank you for the comment, I will try to incorporate some of the suggestions into the puzzle to help with clarity.
1) a. The night-watch is stationary, there are only two paths which you can take that will get you to the wall in the quickest possible way. b. Once in the field of view of the night-watch the alarm will raise and your cover blown.
2) You understand correctly.
3) They are situated on the wall.
I think one factor that was overlooked as a potential for conflict is the developments by Russia and the ongoing push by China to be involved in the Arctic. As you mentioned they are interested in material collection and with the melting ice caps this unleashes a plentiful lot, along with new shipping routes. They have been granted an observer seat on the arctic council and with more military activity in the north with Russia and the rest of the arctic powers, it is not far off that this area will become more engaged here.
(I corrected the answer I gave for the first part, thank you) The answer needs a slight specification in that the r is not that of the night-watches observable field, but r+epsilon, indicating that the spy remains one point beyond the FOV of the night-watch.