Essentially my question is whether I will have to do anything. If I understand the system correctly, the moment the population of Luna exceeds the Infrastructure limit there will be a demand for Infrastructure there, and the civilian shipping lines will jump at the chance to fulfill it using the excess produced by Earth. Is that correct?
Essentially yes, as long as there is a demand and a supply within the civilian freighters range it will try and fulfill it. The population doesn't actually have to exceed the population supported by infrastructure figure, when it starts getting reasonably close demand for infrastructure will appear on the colony.
