Total mass of the asteroid belt is <0.1% the mass of Earth. Total mass of all rocky planets, moons, asteroids, comets, and any other Oort cloud objects is about 3 Earth masses. Not harvesting Earth first if you can and you’re right here would be very odd, until and unless you can build everything you need out of the sun or the gas giants.
Total mass of the asteroid belt is <0.1% the mass of Earth. Total mass of all rocky planets, moons, asteroids, comets, and any other Oort cloud objects is about 3 Earth masses. Not harvesting Earth first if you can and you’re right here would be very odd, until and unless you can build everything you need out of the sun or the gas giants.