Well, if you assume that the air recycling will be done by plants, you are going to have a need for a huge biosphere and probably for a lot of oceanic biome. If you plan on having an agriculture, if you plan on having pollinating insects, you are going to need a huge biomass.

You're going to have far more nature than you will have humans.

This setting usually assumes that you have a fast transport network built in the core infrastructure. So being spread out is less of a problem, especially if you have free electricity through solar panel. That means that moving stuff around on electric motor is going to be basically free.