Wisp will give you the option to 'kick' someone out of your town yes. And then the person you want to move in will plot their house the day after the person leaves.
Yup! I adopted Marshal through that method. As long as its a normal villager (not gained through the figures, like Inkwell or Cece or example, or through the Sanrio cards, like Etoile**,) they can be adopted out!
When I chose to move out Peewee to make room for Mac he went into boxes immediately (he was walking around prior to this.)
I've also read that if any other villager has asked to move/has plans to move forcing a villager out won't change their plans (example: Hazel has plans to move on xx of November and you force out Static, Hazel will still move on the xx of November.)
**I assume this is the case, it's what I've read at least!