One of the things I have been thinking of is a sharp bifurcation of space travel. If you have to get there fast, a fusion torch ship is the way to go. Military, fast freight, and wealthy passengers all would use a torch ship. On the other hand, there's stuff moving in the system that doesn't have to get there fast at all - slow freight, bulk cargo, and steerage passengers - which could use some combination of electrothermal water jets, ion engines, or solar sails. Many of these slow ships could use robotics, and passengers travelling in cold sleep with slowed down metabolisms.
Mercury has two resources, abundant sun and metals. There would be power stations in orbit, and teleoperated/robotic mining on the surface, with the operators on the power stations.
Venus is settled by aerostat cities which are locked into the level of Earth pressure - currently 50 km up. They are basically huge ceramic balloons riding in the sweet spot of the Venusian atmosphere. They are also sowing the seeds of tehir own obsolescense - they are seeding the atmosphere with tailored bacteria which is slowly fixing carbon, sulphur, and nitrogen into the surface, and liberating oxygen and water. This is thinning the atmosphere while making it more earthlike. The dead bacteria will also eventually build up a biotic soil. It's a project hundreds of years in duration, but someday, the people of the aerostats look forward to their descendants living on a cooler, life-rich surface.
Earth orbit is crowded and busy. Billions on Earth and tens of millions on habitats and orbitals and the lunar sub-surface. Earth is in a warmer, wetter climate phase, and abundant power from fusion and solar power satellites means it's getting warmer as well as richer. Population has stabilized after the Birthright Bounty became widespread - by giving up one's right to reproduce, one can buy a fairly comfortable lifestyle with no need to work. Otherwise, each person is allowed to reproduce himself or herself, and some are allotted more - the birthrights of those on the Bounty - for special merit. So Earth rides in the center of a web of trade and information, supported beyond its own means by the civilization of the entire system. Besides, Earth has a beanstalk, and even though it's down at the bottom of a gravity well, it's easy to climb out.
Mars is mostly orbitals. Only science teams are allowed on planet, as the discovery of native Martian life - bacteria and other primitive creatures - put an end to plans for development. Only a few hundred people live on the surface, but hundreds of thousands more live in orbit. Mars orbit is the gateway to the outer system, and the center of its own web of trade.
The Belt is well settled - particularly the dwarf planet Ceres, with its utter overflowing abundance of water. Mining concerns in the rest of the Belt sling their semi-processed ore to Ceres via robotic slow freight, where it is refined, alloyed, and manufactured into everything the system needs. Many rocks have been settled, particularly mined out rocks, and more manufacturing takes place on them and in their neighborhoods.
Jupiter's moons have also been settled - at least the ones outside the lethal band of Jovian radiation. The Jovian settlements are younger than those around Mars or on Venus, though older than those further out, so the societies are an interesting mix of frontier and civilization. One of the biggest assets the moons have is lying on the edge of huge gravity well, which is used for slingshotting and braking, so slow freight is faster and cheaper here than elsewhere in the system.
The moons of Saturn are more recently settled, and smaller than the Jovians, but Titan is a fascinating world, and the rings are just gorgeous, making for a surprising amount of tourism despite the high price tag. The cultures are much more frontier than on the Jovians, though some luxury hotels in orbit are as civilized as it can get.
Past Saturn, settlement thins way out. There are probably more people in the Kuiper Belt beyond Pluto than there are around Uranus and Neptune. This is the real frontier. Past Saturn, most anything goes.