It's a judgment call. I don't think there's one right way to do it. In this case, since the spirit was actually trying to counter-attune to Rune, I used the Fine quality of the spirit mask to reduce the ghost's harm (the item says it protects against possession, so I'm fudging just a bit). If the ghost gets a better idea, and tries to attack Rune another way, the mask won't protect her like that.
Yep, that works. The rules don't really say one way or the other for helping. Either way is fine.
We shall see.
1) It's possible with the right combo of special abilities, but usually, no. Level 2 harm would take at least two downtime activities to clear. (In version 8, which is slightly different than 7.1)
2) Maybe. 2a) Maybe.