[nn3]

If you would spin the whole structure you couldn't have multiple shells all with 1G on their surface. The required spin speed for 1G depends on the diameter. But their whole concept is built around multiple shells, which is clear from the name.

Regarding the GDP needed once you have a working "mine from the moon and send to orbit" economy it doesn't seem to be too bad. The assumption would be that a lot of technology is already developed for other projects. Launching it all from earth obviously wouldn't be possible even with vastly cheaper launch. That's why they put the build into the moon-earth L1 lagrange point to be easily reachable from the moon.

For propulsion and reactors, but there are multiple projects today working on all of this. Building a life support system for 400 years is still an unsolved problem however.

[vl]

Re: orbital assembly. L1 point is bad in every respect. If most materials come from Moon, then the best assembly point is low Moon orbit (as benefit you get a boot to your launch speed to escape Earth gravity), if most material comes from Earth, then best assembly point is low Earth orbit. Hauling all material to L1 is going to be more expensive in either case (unless the ratio of materials is very exact, which is unlikely).

Re: spin. I still claim that the best design is to rotate entire living module as one. Most of the activity is going to be on the outer shell. Warehouses, etc will be in the lower gravity inside. No moving parts.

The only question is what to do with fuel and retro engines. Rotate them as well? Fuel tanks need to be stronger. Do not rotate? Then maybe living module can undock for the flight and rotate separately.