There are already answers to many of these questions.
A lot of people have worked on the technology of moving asteroids, refining on site, transportation, energy needs, propulsion techniques, and cost/benefit.
Obviously, we have a ways to go before asteroid mining is a major source of resources, but we already know where a lot of the nickel-iron asteroids are.
Here's one.
Forty years ago nobody would have thought that it would be cost-effective to haul oil up from under a mile of ocean, either.