I have some questions about mystery island villagers

[TROPULOUS]

Can we get villagers from mystery islands after the initial 3 we can get? And if so do we need to have an open plot of land for them to appear on the islands?
I'm sorry if these questions are obvious but I don't wanna waste my nook miles tickets D:

 

[Jam86]

if you have a plot of land open on your island then they will show up