Whatever you do, please, for the love of Roddenberry, do not put a population size under a billion on a planet and have them bitch about not having room to share. I swear, if I came to resettle a population whose planet exploded and got that answer from the existing colonists, I'd wipe every last one of those entitled whiners and make it the refugees new home world.
I've recently been re-reading the original Little House on the Prairie. The book starts when it's getting too crowded near their house (In The Big Woods). The author describes the family's amazement at seeing people pass near their house "almost every day". The idea of just seeing (not interacting with) 5 people a week is motivation for the father to move the family from Wisconsin to Kansas.