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.