I am going to be asking a series of questions that will be relevant to forming some sort of a picture of human space commerce.
Let's say that Earth-based human civilizations have discovered a series of ancient jump-gates that allow them to travel within a large and varied interstellar network.
There are not many clues, apart from the jumpgates, as to who left this system behind. For the moment, I am assuming that there is no bias to the kind of systems included in the network: i.e. its not like systems with earth like planets make up the majority of the planets in the network. So, "system types" have roughly the same probability of occurrence as if one were just taking a cross-section of space and scanning it.
Put another way, the gates simply connect a large number of close-by star systems, rather than a large number of only useful star systems.
While genetically-engineered humans exist in this "universe", no sentient non-human aliens have yet been encountered.
If a space faring civilization can build space stations, why would they ever bother with planets?
For resources, space stations could be built around asteroid belts. Otherwise, space stations may be placed in almost any orbit or other stable configuration.
So, what might planets offer, that stations simply cannot? If terraforming technology exists, assume that it is time consuming (centuries).