So in short :
As it was said before, base habitats are not great but they can be upgraded by adding major and minor orbitals over celestial bodies.
All orbitals will allow you to build up to 3 buildings of all the base ressourses and research that should have been collected. Let's note that it seem that those ressourses are no longer collected by the space station which mean that you should avoid doing so before you can garantee the jobs are used (and also is does not matter if 3 or 15 physics are collected on a celestial body, you will only unlock at most 3 labs by orbital, same for energy and minerals).
Only major orbitals increase your district cap and those will be more efficient at doing so when you upgrade your station (which is now done by upgrading the planetary building and require both the habitat tech and enough people).
It's best not to "pre-build" all orbitals in a system as you will just end with empty districts and you would have been better of making a habitat in an other system, increasing your total pop growth.
Minor orbitals don't increase your district cap so don't build them if you don't need the specific districts they provide. In particular, while possible it's useless to build an orbital on a minor body without ressourses.
And an other specificity : Alloys and very rare resources are directly collected by the habitat if you put a orbital on them. Rare ressourses (gas, motes, cristals) will instead create directly one job to mine them (which will usually be way better than the station that collected them before).
