First, understand trade hubs are really more supply hubs. There doesn't seem to be a true economy amongst your planets; there does not appear to be an economic system underlying trade. Planets are sinks and sources for commodities and components.
Defining a couple of terms:
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[*]Commodities are trillum, hexacarbide, chronimium, organic food, durable goods, luxuries, ctholon, and aetherium.
[*]Components are starship reactors, jumpship drives, ship weapons, armored vehicles, and exoarmor.
[*]When the distinction is not important, I refer to components and commodities together as trade goods.[/list]
Outside of trade hubs (and under the Trade & Enterprise doctrine, capitals) the designation of a planet determines what the world will export. Planets can import anything.
Trade route % can be controlled by clicking on the route. You can set the % to be anything from 0 to 999.9%. It would be unusual to set a % higher than 100, but it is not at all unusual to set a % to 0. For instance, if a world is about to be captured you might set the export % to 999.9 to try to remove as many trade goods as possible before your world falls. On the other hand, when connecting a consumer goods autofac on an ocean world to a trade hub, you might set the durable goods and luxuries to 0, to allow the world to concentrate on producing food, for which ocean worlds receives bonus production. This can allow other CGAs to focus on durable goods and luxuries.
Starport %: appears to have no affect. Others have reported that when the starport % falls too low, below 10% or 5%, trade disruptions can occur. I have neither tested nor observed this, though I nonetheless keep the % above 10.
Trade hub tech level: trade hubs do not seem to trade in ship components below their current tech level. They will trade all commodities. [NB: have not verified ctholon and aetherium tho] Put another way, a TL5 hub will not supply basilisk cannons between a TL9 starship autofac and a TL9 starshipyard. That same TL5 hub will trade chronimium, which requires a TL7 world to product. After testing, I just couldn't get a starship autofac to transfer components through a trade hub. I don't know why it wasn't working in my case, but it ultimately did not seem to be impacted by the TL. This seems like it must be a bug.
Only one source on chain: when you link trade hubs together, you may notice that commodites at one end are not being distributed to worlds at the other end. That is:
[code]Trillum Extractor with MILLIONS of trillum --> Trade Hub --> ... --> Trade Hub --> World that needs trillum but isn't getting it[/code]You may find that the world that needs trillum is not getting it. What seems to reliably resolve this is putting another trillum extractor at the end of the trade chain. That is:
[code]Trillum Extractor with MILLIONS of trillum --> Trade Hub --> ... --> Trade Hub --> World that needs trillum and is getting it
`-> Trillum Extractor with not much trillum[/code]This may be a bug.
Setting and resetting trade networks can sometimes help situations where things don't seem to be working correctly. This is almost certainly a bug. When you do this, what seems to work is this:
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[*]Cancel the trade route.
[*]Wait at least one turn (a "watch").
[*]Restablish the trade route.
[*]Optionally fiddle with the route's %'s.
[*]Be careful! Ending a trade route that is supplying a large % of a world's resources can cause shortages that are difficult to manage. You've been warned.[/list]
If you have information about making more effective use of trade hubs, or if you have noticed problems that others can avoid, reply to this, and I'll keep this updated.
I'll add a bit on trading with Mesophon soon.