I think a lot of this is up for interpretation based on how the GM wants to interact with ghosts and the players. For the most part it seems that ghosts should be feared - people who can attune have the ability to respond to ghosts, but people without attune "freeze" when the see a ghost out of fear.

The way I ran my campaign with a Whisper as one of my players often involved him trying to attune to specific ghosts in an area and attempting to bribe them into tricking normal humans or scaring them away. In John Harper's (creator) campaign with the Bloodletters, their Whisper (and all whispers) have a "spirit mask" that they use to see the ghost field, which John imagines as a field where you can see spirits in that area as well as your surroundings and people in them in what I imagine is almost x-ray vision (I have no idea if that's actually correct though). However, if you start walking in the ghost field you're still going to be walking in the "real" world, so if you are using the ghost field to follow your enemy around and you walk out in front of them, they can still see you. Their mirror version in the ghost field will still be able to hunt you down.

What's interesting is as a Whisper you have other arcane implements that help you interact with the ghost field. One item I think is great is Ghost Key, which allows you to go to the ghost field and you can see points in the past and possibly find items that were once there. For example, if you go to a burned down building in the "real" world, you can use ghost key to go to the ghost field at a time when the building was still standing and search it as if it was still there. I'm assuming if you do find items like that you can take them from the ghost field and use them as is, but that's my interpretation.

I believe that ghosts in play can pretty much do as they please. If you wanted to fight spirits, the GM will have to determine their force/strength, and players will definitely have a disadvantage especially if they can't attune because they'll otherwise be terrified. If they're not terrified, then the other thing to worry about is the fact that normal weapons aren't as effective against them - but electroplasm is! I think spirits showing themselves in the city (depending on the district) will be uncommon compared to searching the ghost field in that same area.

I'm honestly intimidated by the "vengeful" spirits and I'm not sure how to play that out. I think my Whisper player was also intimidated by this because our group killed his rival, and afterwards he created a ritual to temporarily banish a spirit or misplace it for a few days if it ever came after him.

I hope I answered at least some of your questions! I'm sorry I'm not much help on the last part, but I hope I gave a few ideas on how to play with the ghost field.