

Saturn V was done with the resources of a nation behind it, because they had to beat the Soviets. That rocket also only went up, and was not reusable, with a tiny fraction of the Apollo mission hardware returning to Earth.
All of this with less computing power than some egg timers of today.
There was considerable computing power on the ground supporting the missions.
Plenty of metals floating around in space. Just need to go and get them.
Only need to capture one decent sized metalliferous asteroid from a near earth orbit and we’d be set for a century or two.