The Tribunal is a zero-g faction. As a result they are unable to colonize planets. Instead, they create massive super structures that their people live on. These super structures leech FIDSI from the planets in the system. They can have half as many structures as there are planets in a system. They can leech from any planet without research of the planet type. To balance this, they receive no anomaly bonuses and are unable to collect strategic and luxury resources. The Tribunal can construct a "Seat of Power" (SoP) in any system that is colonized by a different player. The SoP is a center for diplomacy and trade, with it the Tribunal provide benefits and detriments for the system in exchange for luxury and strategic resources.

 Ex. pay 30 influence. -20 happiness to system for 10 turns, unless the systems owner provides 10 dark matter to the Tribunal

The SoP also provides unique diplomatic actions on the systems in which they are located. Or against an entire empire if every system in the empire has a SoP.

 Ex. pay 50 influence. Intercept and perform the next diplomatic action for the target faction

Cool idea for a race. However the ability to make demands through the Seat of Power seems similar to what is already possible for all factions through the system of diplomatic demands. Also, why would other factions allow these SoP to reside in their system? Wouldn't the be attacked? How would they be defended?

Also, I suggest laying out the faction's traits and affinities in a list to make things more clear, like I do here.