You won't be able to get 2 of the same person to move in. And there is a like waiting list before they can move back to your town. As for speaking with them, it should be the same as normal, you'll have to introduce yourself 1st
Yeah, it's like they're a totally different person, just like in previous games. It makes sense even though it can be weird.
What I really hated was how in City Folk if someone moved away and then you saw them in the city they didn't know you. I always thought that city-goers ought to include your old villagers!