First part is correct. Sorry if I wasn't clear. Yeah currently have nine villagers with one moving out to make it eight.Correct me if I'm wrong. From what I understand, you have nine villagers and one is planning to move out. So after they move out, you'll go down to eight? If yes, you can adopt even during that span when they haven't moved out yet.
If you have 10 (counting the one who wants to move out), you need to move them out first to have a space to adopt someone.
Thanks for the answer. Now I can adopt fauna!