You are going to need other elements for some stuff occasionally. Perhaps you can mine dust.
The impression I get from reading it is that he figures either teleoperated mining robots, or mining the asteroids; he spends more than a little time on discussing the great leaps in robotics, and then in claiming that a Venus colony is, from the point of view of orbital mechanics, almost as good as actual asteroid colonies for traveling to & exploiting asteroids.
Seems to me like Mars is probably the best colony world. Much fewer engineering problems, I think. And IIRC Martian soil consists primarily of iron ore. Plus way more water.
Teleop mining robots? That place kills our probes and I don't think they even have many moving parts. What about some kind of bucket chain?
I was wondering what people thought of this paper by Geoffrey Landis on colonising Venus. In it he suggests that cloud-top Venus is one of the most benign environments in the Solar System. Temperature and gravity are similar to Earth, there's some radiation shielding and useful resources, and aerostats filled only with breathable air would float at that height. I'm no expert so can't speak to how accurate it is, but it's certainly very thought-provoking for such a short paper.