On I think day 3, Tom Nook will ask you to help him create plots for villagers to move in regardless of whether you’ve invited any already. I think you need to wait for this to happen before they can move in.
Nook will have a phone call in the morning announcement, after go to the tent and he will ask you to help him set up plots for new people and do stuff, then they will move in the next day. but you need your museum up and the nook shop too till he asks you for help.