The Last Stand mod will feature space stations similar to what you describe. However, some of the stuff you mentioned might not be doable right now.
For example, unless I am mistaken, the constraint system used by the game relies not on the actual number of units or buildings built, but on the amount of slots they take. So since an orbital superweapon takes up 18 slots, and any planet has max 35 slots for tactical structures, it is impossible to have 2 cannons in orbit. But should you increase the tactical slot count of a planet (or decrease that of a cannon) then you could easily build more than one cannon.

Same with everything else. Currently there are no numeric constraints which allow only a set number of ships or structures to be built, with a few exceptions like refineries, but they are hardcoded in their type and cannot be applied to other units or buildings.

Furthermore, tactical and civilian build slots are tied to the planet entity types. I do not know of any buff or structure which changes that, so it may not be possible right now to create a station which increases these slot counts. Not to mention that because of the abovementioned constraint system, you would end up with a "super-spammable" building, a building which not only does not occupy any slots, but makes more of them! The AI would go berserk with that...

Anyway, my mod will have stations used for sector defense, adding fighter wings, long range fire support and close range defenses in one lethal, but costly package. Not to mention that these stations will be deployable in any gravity well, even those around stars and uncolonizable worlds and objects.