If you StreetPass or visit friends a lot, it might be tough because you could end up taking a villager moving out of those towns. I'm not a big fan of how that works, but it could happen.
Not to my knowledge. I think you can delay it using the same method as the villager reset trick (only this time you're interested in there not being a plot at all, not whose plot it is) but I think after a certain number of days the game forces a 10th villager on you.
EDIT: What I stated above is for when you have 8 villagers (so the game forces a 9th on you). My memory is failing me lol