How to fill a new Habitat?

Let's eat this elephant one bite at a time. The question was about the
steps of moving into an average everyday Island 3, not the entire path from
today till then.

As for the rest:

Getting people into orbit: maybe SSTO hypersonic planes, maybe the space
elevator, maybe a magnetic catapult with a tolerable-G acceleration, maybe
something nobody has thought of yet. No way to say, because the
innnovations are still being done. What if we were asking these questions
100 years ago about the mathematics behind modeling a thunderstorm--nobody
could conceive of the supercomputers that can now take a stab at this
problem? It would seem pretty hopeless.

What's the financial route: An excellent question, one that doesn't get
asked enough. I honestly think it'll evolve from the rich, first as orbital
tourism, then orbital timeshares, then permanent residences. Then as
companies compete for that premium dollar, costs will go down, and the whole
thing will unroll a little at a time. The timeline I presented assumed a
mature habitat-building industry, with asteroid mining and the construction
of most of the equipment (solar panels, wiring, computers, processors) done
in space. In other words I simplified my example with some assumptions.

The financial commitment of immigrants: Hey I always thought indentured
servitude wasn't a bad model. It's just a different name for a 30-year home
mortgage anyway.

I don't know if the Virginia Company ever made a farthing of profit, and the
East India Company seemed to be forever in debt. But the social changes
they wrought were remarkable.