For humans to be self-sufficient in space, we would need to be able to make log term commitments and some initial investment. But if we do it right, cost to the Earth would go down.

They asteroids probably do not have all the resources to be 100% self-sufficient. They would still be an import source for resources and a gold place to start. They could supply the human race with building material for just about anything we need in space.

Mars is probably the only place humans could be totally self-sufficient with our current level of technology.

If we would set some goals, such as the ones I write below, we would have a great chance at pulling it off.

Goal #1: Study the asteroids. This goal has 2 parts
Part 1: Study the Asteroids for their resource potential. Also tacked on to this goal is to study and develop machines for mining and processing the asteroids resources. These machines could also be modified for the Moon and Mars.
Part 2: Study the asteroid for ways to move them out of harms way. I prefer potential hazardous asteroids be mined until there is nothing left to be a hazard.

Goal #2: Set up a space station that acts as a way-station between the Earth and NEA’s, Moon & Mars.

Goal #3: Study the Moon for potential resources and how to mine them and process them.

Goal #4: Depending on the results of the Moon and NEA’s resources and how to mine and process them, build a space base industry for using space based resource to build ships, probes, or whatever we need up there. This could be located in LEO, on the Moon or in orbit around the Moon.

Goal #5: Continue to study Mars for human habitation.

Goal #6: Used the information, technology and space based industry to get humans to Mars to stay.