re: delta V, the chaotic nature of orbits involving many bodies means that a very well-timed nudge ought to be sufficient to move certain asteroids quite a long

re: delta V, the chaotic nature of orbits involving many bodies means that a very well-timed nudge ought to be sufficient to move certain asteroids quite a long distance for "free". So the problem becomes finding the right asteroid, and the right time, and the right nudge vector. More about computation than rocket fuel: the deeper into that chaotic system we can penetrate, the less we have to spend on influencing it. You've also got to slow it down when it gets to where your smelters are. For that I'd propose we just let it smash into the moon and then mine it on the surface. We can alternate which sides we smash into in order to prevent the moon's orbit from changing significantly. Of course you still need to provide the initial nudge, which ain't nothing, but it's a far cry from towing an asteroid or towing a smelter.