> There are very few buyers that have the capabilities of using material produced in space, ... There's no manufacturing in space yet. ... build said manufacturing capabilities

Well, I'm working on that. Check the "view history" tab on any page of that book to see who wrote it.

All your words that I quoted above are correct. Aside from robot arms and a 3D printer on the ISS, there is essentially no industrial capacity in space yet. Factories of the kind we build on Earth are too heavy to launch into space. So how do you get started?

A "seed factory", as I describe in that unfinished book, is a starter set of machines and tools that are used to make more machines to expand itself. This is where asteroid metal and carbon come in. Iron is by far the most important industrial metal, and 98% goes into making steel (iron with added carbon). Metallic asteroids are already in native form. They don't have to have the oxygen removed like iron ore on Earth.

The added machines are first to increase scale from the starter set, and second to make machines that work with other materials (glass, aluminum, etc.). You will still have to deliver some materials and parts from Earth while you bootstrap, but a lot less than if you tried to bring everything from Earth.

The starter machines can be as light as 20 kg, so certainly a single 100 ton Starship payload should be able to deliver a functioning machine shop with usable capacity.

You wouldn't jump into this without doing some R&D. We need to fly some asteroid retrieval missions in the ton rather than ~1 kg range coming back on the Osiris-REX mission. Ideally you want several different asteroid type samples. Then you feed those materials into pilot-scale processing machines and figure out what works and what doesn't.