Hi, the space station system is fairly straightforward across EAWX mods.

There's 5 main space station levels that sort of work like the vanilla stations - they fill the main slots that you can see on the galactic map if you have the planet info filter on (which you should always have on in any mod). Different factions have different space stations models for each level, but they're all roughly equivalent and each faction has 5 levels, but up to which level you can build is dependent on the planet, just like in the base game. These main stations are what allows the secondary stations to be built and they also add to your infrastructure score. Main stations have a silver border.

The secondary stations encompass additional defenses, the shipyards, and economic structures.

Shipyards are the simplest: To build ships on the galactic level on that planet, you need a shipyard. You can only ever build 1 shipyard per planet, and the exact type/level of the shipyard is dependent on the planet - similar to the base game. There is never a reason not to build a shipyard unless you don't have enough money. Shipyards have a blue border.

Additional defense stations are unlocked with the main station level. You can only ever build 1 additional defense station - if you then build another, it overwrites the existing one. They can be useful to defend but are rarely a priority. You can check the stats in the build menu to see which station might be stronger. These have a bronze border.

The economic stations are where you have the most choice: There's tradeports, small colonies and big colonies to build. Colonies give you extra max pop cap on the galactic map (so more ships and units you can have on the galactic layer in total), while trade ports increase income. Some planets also have orbital mines that also increases income, but in a different way. You can only build one economic station, either a trade port, or a colony, if you build another, it overwrites the previous one. Trade ports and orbital mines have a gold border while colonies have a purple border.

If you have 1 shipyard, 1 defense station, and 1 economy station at the same time on a planet, that planet gets +1 influence, which is good. Which stations it has doesn't matter for that, only that the planet has 1 in each category. If a planet has only a main station level 2, you don't unlock any secondary defense stations, and you get the bonus just by having a shipyard and an economy station.

And that's the basic gist of it. It's all fairly simple. Just build new silver ringed stations when you can and then check which secondary stations you currently need.

Addendum; you can only build secondary defensive stations that are two tiers below a primary; if you have a tier 3 primary, you can only build tier 1 secondary, but that goes up to a tier 2 secondary if you (are able to) upgrade the primary to tier 4.
Hapes are able to build 1 tier below instead of 2 tiers below (so a tier 2 secondary with a tier 3 primary, etc etc)

Orbital Mines are currently not in TR, but will be added in 3.5 - you can find them in FoTR and RevRev for the time being.

Some factions (Hutts, Zsinj, CSA) are able to build alternative shipyards; for the Hutts and Zsinj it's the pirate base, and for the CSA its the shipmarket. These still count as shipyards for the purpose of infrastructure and influence, but simply offer alternative build options.