Considering it's moondust and thus has to come from the moon, also assuming rocket engines have gotten more efficient since we last sent people to the moon and taking into consideration the much lower gravity of the moon. I would hazard to guess that it would take about the same or less fuel than an Apollo mission. Also, once the container was launched from the serfice of the moon you could probably propel it using a light sail and some sort of solar powered beam thus only needing fuel for take off and deceleration. But that's all just guesses based on unbacked assumptions.

If you were to launch it all from Earth it would be about 100 tons of cargo for every million kg of methane.

A million tons a year to orbit (10,000 launches) equates to 600 billion cubic feet of methane, or about 2% of total US annual production.

But the actual plan would involve manufacturing the “mirrors” from moondust and propelling them to L1 using railguns powered by lunar solar panels. So you don’t need nearly so much methane.

Impossible until it’s inevitable. The material is available at low deltaV from near-earth asteroids. Though it’s better fabricated into a giant solar sail of a sunshade.