The game will automatically give you random move ins (random villagers on random days) until you have 9 villagers and there is nothing you can do to stop this, but don't worry it normally takes awhile for the game to move in villagers randomly, so you have a bit of time to look for your dreamies. Normally the random move ins will stop after you have a town of 9 villagers, it is rare but I have heard of the game giving people a 10th random move in (like super rare for the game to do this on it's own). As I mentioned earlier the game will slowly move in villagers once you have started the game (like one or two a week or less? if I remember correctly) however if you streetpass, visit someone, or someone visits you (like a trade or something) you can get a voided villager from them, a voided villager can move to your town as long as you don't have a full town, they can even appear as your 10th villager. My best advice would be to not streetpass or visit with anyone to decrease the chance of getting a voided villager, I would also check to see if a villager pings you to move and if you don't want them in your town accept their move out dialog and ignore them until their move out date (so they don't change their minds and want to stay) to free up more space in your town. I think you should be ok, it is relatively easy to move out villagers if you need some space, plus most users on this forum are super nice and I think if you are full on space when trying to get a dreamie some users will be kind enough to wait for you to move out a villager.