Too many rules and steps stifles me. The 3I is a massive juggernaut, with an amazing tax base and thousands of SDBs in even minor systems. Interplanetary trade is robust. Many starports are huge city-sized affairs. The 3I is a powerful force to reckon with, with good control over most of its member worlds and the power to back its authority.
Interplanetary trade is good on many worlds.
Starports are planetary trade centers. The 3I is a stable confederation, held together by the nobility of its population, but not all-powerful and overall not wealthy. Interplanetary trade is regular. Starports are common. The 3I is a loose, vulnerable sprawl of worlds, which by the way is no worse off than the other interstellar states.