I cannot agree with (4.) "You [..] need to bring back the entire asteroid, which would require a massive amount of delta-V".
You don't need a rocket nor fuel for the full delta-v to put the asteroid into a near earth orbit. Look how mars probes arrive: just use a tiny rocket motor to steer into the athmosphere and perform aero braking. Takes long, could even take years to reshape the orbit, but it doesn't neccessarily take much fuel. I'd just place a light-weight ion engine on the asteroid.
You don't need a rocket nor fuel for the full delta-v to put the asteroid into a near earth orbit. Look how mars probes arrive: just use a tiny rocket motor to steer into the athmosphere and perform aero braking. Takes long, could even take years to reshape the orbit, but it doesn't neccessarily take much fuel. I'd just place a light-weight ion engine on the asteroid.