One of the common idea’s in science fiction is that when people leave Earth and go to the stars we will be living mostly on planets, often terraformed ones.
The thing is that there are many other places we could live, terraforming a planet to live on is probably the most inefficient and expensive solution to the problem. It’s like erecting a mountain so you can live in a cave.
It would take much much less resources to build enough habitats for a planet of people then to make a planet able to support them. You also will be putting all your eggs in one basket, you screw up your planet and you could lose billions of people and centuries of work.
Its not like on Earth we are all crowded around a few good spots and ignoring the rest of the planet. People live everyone on earth that can support us.
You might have mining around the asteroid belt. Manufacturing and some mining on the moon (where you can use a rail gun to launch what you make to anywhere else). Hydrogen is not easy to get in the inner solar system, it may turn out to be cheaper to import it from the gas giants. This could mean large bases that turn into colonies on the larger moons.
In the solar system earth’s head start and livability means that it will probably always have more people then the rest of the system but that would not apply to any new systems we go to. I could see the planet being more suburb then city. You don’t really mine or make anything on it because it cost too much to do so. You use it to raise you kids, and to relax.
It would not surprise me if there comes a time when most of the human race has never set foot on a planet and probably never will.