Nice work. All things in life revolve around Energy. I would expect advanced civilizations to have more advanced means to collect energy from stellar platforms. Microwave beam stations, bussard collectors, orbital reflectors perpetual motion electro-gavitic generators are a few advances over solar panels.

I though about the Trading Hubs (the +4 Energy Modules) and the Offworld Trading Company (the building which increases their output to +6 Energy).

My personal impression is that those Modules/Buildings are currently in a tuff spot. But I'm not sure if there is a good balance between buffing them (to perhaps +5 Energy per Trading Hub and +7/+8 with the Offworld Trading Company) and not making them too OP or stil being in essentially the same tuff spot where their resource output doesn't justify them taking up valuable space on limited starbases. This is also more of a nitpick but: I dislike putting more resource production into Starbases, the categories work but you for example don't just see what their purpose is when in System view (and adding an indicator for Resource production like Megastrcutures have seems to be impossible), besides their level and military strength they are blackboxes which I don't want to move too much of the economy into.

Beyond all that:

Between planetside production, mining stations in space and a Dyson Sphere - I'm kinda missing something mid sized here, like a Habitat relative to a Planet and Ring World. Making a Starbase Building/Module (combination) which fills that gap would be easy...but personally I would prefer an in-space object, which can be seen and ideally also be destroyed.

Solar Collector (Defense) Platforms should be doable (although I have no 3D modelling skills, so that would mean reuse of exsiting models) but personally I'd favor a energy collecting equivalent to the before mentioned Habitats which could be built over suns. Not sure If I'll ever persue that idea - considering my missing 3D modelling skills - but we'll see.

I think that trading hubs should be buffed. The numbers that you suggested would be perfect!

Personally, I think that nebula refineries should be put back down but put them as a module, not a building, like trading hubs. Or add a new module for that, and turn them into an offworld trading company-esque building that adds minerals to the new module.