I don't populate the world, i just start with the premades. But I'm always struggling with mccc population. I haven't found balanced settings yet. My world is so full and everything is a mess and im only in the beginning of the 3rd generation. I mean i can't recognize the fouding families anymore. They mixed with homeless, everyone had kids... it's complicated.
I don't want to loose my played sims progress so i won't start again, but i will change settings again. I had teen pregnancy on, but i will set it off; i will only allow marriages between townies and only YA and A. I will only allow 2 kids per household max...
If i could i would delete all non played sims and put back all the premades, but i think they aren't in the library or the gallery.
EDIT to add that it's being really hard to find single sims in my save right now. Not really hard, almost impossible. Everyone is getting married super fast. It may seem that i have my settings very loose but the truth is that i have downgraded marriage and pregnancy percentages a lot below standard...