Populating custom world

Resident immigration and, in particular Rapid Immigration to populate a world right away, would be functions of NRaas StoryProgression for those so inclined, not MasterController. :)

Without mods to move things along, EA's story progression may or may not move some sims into an unpopulated or mostly unpopulated world. Even if this is intended, it often does not work or is not exactly reliable.

I use pre-made sims from CAS to make residents for unpopulated towns. Sometimes I swap genders or ages, so my towns won't have all the same residents, and I randomize traits and names. For families with children, I create them with genetics in CAS. It's quick and easy to make a bunch of households that way. It takes longer if you want to be picky about their outfits. I don't know if the game will assign careers if you don't have any mods, but NRaas Story Progression will take care of that for you if you have it. You might need the careers module for that too. I always do it myself, but again, that will take longer, and you need NRaas Master Controller to do it.

I save families from all the worlds I like then place them in the world.

I do the same as @leetamme. Some with their houses, but mostly without, because it´s easier to place them. I have quite a selection at this point. :D

I have certain family from different sim worlds that I love and I always put them in my new towns. Somehow they just feel right an I love to see them around town.

You could either make a bunch yourself and then add them in or I believe NRaas master controller mod would do that for you too

Okay thank you! I play with both Story Progression and Master Controller from NRaas so I’ll play around with the settings