I was thinking in terms of Coruscant where it could be the "first" and "last" planet.
For example, it's your beginning planet as you're a padawan at the Jedi Temple. You're given menial tasks (fed-ex type padawan stuff) across Coruscant, and in the process you come across the seedy side of the planet (crime organizations, bounty hunters, cantinas, etc) and take on those missions if you choose. Eventually, you get summoned before the Jedi Council (no clue who is on the Council or how they'd explain it, but for argument's sake, there is one) when you've proven your worth (X number of quests completed, and/or X levels of experience gained) and sent off on the mission (whatever the main story arc of the game is) to a different planet. Fast forward to the crisis point, and you have to return to Coruscant to face whatever final enemy you have to encounter.