Well if you have water and energy then making food is simple as well - you have hydroponics, with sizable human population you would also have a lot of natural fertilizer, plus most of artificial fertilizers are based on nitrogen which I assume isnt so hard to come by in space either. What is the technology level in the energy area? Do we assume that nuclear fusion is functional and accessible enough to be used in such distant colonies and harsh environments? Or do we stick with solar, geothermal (where applicable) or regular nuclear reactors? What about spaceships, what fuel do they use? Do we stick with the current system of hydrogen-oxygen reaction, which would mean the ships would have to stop and refuel or do we go with something more "star-trekie" like and kinda blackbox it into "well there is the engine that moves us through space, it works and doesnt really need anything". I am trying to figure out what would the nations trade amongst each other - if the fuel system was in place, I assume the colonies occupying frozen worlds such as Jupiter moons (which was my first thought at a nation) and other ice-comprized bodies could become big fuel refineries, trading it for other things less accessible on their worlds, such as metals, which would be mined from asteroids.