Creating clean -renewable- energy on Earth,in Space,or in Space Colonies for usage in either one of those,is important in having long-term growth for the space colonization efforts.
With Solar Energy,which we can create in each Solar System, we have almost unlimited acces to solar energy. What we need is to come up with a way to efficiently store the energy,like in a battery. This battery can be picked up and replaced automatically by one of the Space Vehicles from a sattelite-based or planet-based solar energy farm. It could also be possible that the energy is transmitted via laser,between a Laser station and Solar sails. To gain as much energy as possible,we should not only have solar-sattelites,but also have solar-panels on Space Vehicles,Generation ships and on the roofs of Space Colonies.
ElectroMagneticPulsar Energy might also be a reliable energy-source.
We should not focus or restrict to just one or two ways to generate energy. We should keep inventing new ways to create energy,that way we will always be assured of enough energy to maintain our growth and succes.
Another possible way to create energy is Vacuum energy
In some cases warming up a planet,might be necessary to make it habitable by humans. But on some planets it's possibly destructive,like on Earth. An important part of Terraforming is "Enough is Enough". Meaning; at some point the Terraforming -or at least parts of it- are doing more evil than good to the planet. We must be able to 'catch' CO2 in the atmospheres of planets like Earth. When a particular ammount of CO2 is caught,it can be 'harvested' by one of the Space Vehicles,which then go to any other planet and release the CO2 in its atmosphere.