Science fiction ideas
This means inhabited space will be filled in more densely and characters will really only know their local area. The extent to which the Universe is inhabited won't really be known once the civilization gets large enough. The first lunar colonies will have excellent communication with Earth and visit home regularly, but when it takes maybe 10 years to get to the Alpha Centauri system, people will only know their own neighbourhood. Some people will live their whole lives in ships (city-ships, I suppose) and I suspect they will only move when the situation where they are gets really dire or there is some nasty advertising trying to convince people that shipboard apartments are really trendy right now.
The outer space people will first be companies and maybe some expanding countries. In time, companies will seem like fascist countries as regulations become laws and people are born into the company (because if your workplace is your landlord and only source of food you're really stuck with them and you can't really go anywhere). The asteroids will be slowly mined, people will slowly fill the Solar system and other systems as we go.
I'm not sure that terraforming is as easy for me as it was for Asimov, so my planets would all be domed, even eventually becoming like Trantor. I don't mind putting in windows but I imagine that would be very scary at first.
I wonder whether my characters will lead lives of relative drudgery or whether the whole thing will actually be set up properly to begin with. I suspect that it depends on who they were on Earth and who they shipped out with. Some might work to a plan where everyone lives well, but others might just take a cheap ticket away from a dying Earth to a richer land where there are greater resources.
What plants and animals would be saved? Where would they go?
What would everyone eat?
What would they do for air and water?
Is there a solution other than biosphere is what I'm getting at. And for a large enough biosphere I think it's quite reasonable to take spare air on a rocket mission.
This is the universe. The book will reflect our attitudes to it. I need to do a lot of research on how people consume resources and how we change our environment to suit us. I want to also look at how we arrange ourselves into social and economic structures in various circumstances. Finally, there will be an investigation of culture shock, and how people handle cultural differences.