What will they do?
I just wonder what all those million people out there will do. Not initially, obviously, as I'm sure they will be building and sciencing and exploring and, well, populating. But after a while I'd imagine a lot of them would get terribly bored. I mean, here on Earth we can go to the beach, climb a mountain, visit beautiful and exotic locations, play golf, do gardening, whatever, literally thousands of different things we can do outdoors and in. On Mars, you're basically stuck indoors all day watching TV. Oh sure you can put on a suit and go explore the planet but it's all basically the same wherever you go and, whereas a holiday to the Namib desert might be exhilarating the first time, if that's the only holiday you can ever have you're going to get tired of it pretty quickly.
I guess a million is a large enough group that there will be incredible diversity of people and skills, and over time they will come up with all manner of entertainment and pastimes, probably even some that cannot be done on Earth, but you're going to have to choose a million indoors-type people because most, I would think, would still occasionally enjoy being able to look out over a different landscape.
Long term I don't worry so much. If they and succeeding generations make it, they could in time build huge structures to contain enough of an atmosphere to replicate some of the outdoor activities we take for granted, but I doubt that could happen for several decades at least. It's those first few decades before you can get the big stuff in place, that I wonder about.