At around 39:10, Kinggath said, "...since this settlement seems to just keep growing, forever...". In my current playthrough, I'm seeing the same thing with Starlight. I think I'm at 60 settlers there now, and I haven't yet unlocked Outposts!
The HQ portion is not very intuitive. I am having a hell of a time getting living quarters built, let alone recruiting other NPC's to continue making progress with the HQ quest.