[Chris2048]

But the outer planets have excesses of hydrogen, so round trips could help there?

The upside is, of water aka H2O that we need, the 2 H atoms are the lighter component, specifically:

2H = 2 * 1.67 * 10(-24) grams 1O = 1 * 2.65 * 10(-23) grams

So hydrogen is 11% of water, and oxygen is 88%;

meaning every kg hydrogen can combine with 8kg oxygen to give 9L water.

So all the Oxygen already being there (in CO2) is good.

[HPsquared]

If we were capable of planetary-scale transportation of materials, we wouldn't really need to live on planets anyway - it'd be a rather moot point.

[Chris2048]

Space stations would also be practical, yes, but I'm not sure how desirable they'd be (for long-term habitation). Also, we don't really know the long-term effects of low gravity, whereas earth and Venus have similar gravity wells.

[XorNot]

Transportation no, but with large enough reflective surfaces we could redirect comets to impact courses on Venus.

Early stage terraforming need not be too fussed about collateral damage from multiple extinction-events (and the footage I presume would be spectacular).