Thank you for this interesting interplanetary human colonization fiction.
Today, the richest 10% on earth (= mainly the Western end-customers) use approx. half of the planet ressources. And we already face huge environmental problems. Therefore, there is no way that the poorer people will ever reach even half the level of our lifestyle. Because it would require several planet’s ressources to do that. But, as they legitimately want to improve their life, the destruction of the environment is necessary, with further severe extinctions.
And I ask myself : why should we even consider exporting our mess off earth ?
Also, if our interplanetary plan « only » regards our solar system, we have plenty of time as the sun will burn the earth in a few billion years …
I remember that, in the army, they insisted that, in order to achieve the goal/mission on land, we had to make sure that enough men were kept alive until the day of the action.
So, to me, the Big Goal is the one you mentioned : « How sustainable must we become? ». And the first things to consider are indeed to answer your questions : « What is the point of continually growing the world economy?Why should we continue to raise the standard of living? »
That is a huge challenge ! And it needs to be addressed within the next decades !
But it is ALSO desirable to dream of sending a few dozens of people with the mission to create a new breathable athmosphere on another planet …