Unlock Darth Maul
Enter "H35TUX" as a code to unlock Darth Maul for purchase.
Unlock Luminara
Enter "A725X4" as a code to unlock Luminara for purchase.
Hints
Begging At Dexters
Dexter's Diner, where you select your stage/missions is a veritable loot heaven. Your characters never lose money if they die at Dexter's Diner, so each time you complete a stage, walk around the place with any Jedi character and force pull studs from all the objects around the hub level.
Cheese-Kill Anakin Skywalker
In stage 3-6, have a second player take control of the boss and force the character to jump over the lava pit. Just before Anakin Skywalker hits the lava, have the second player hit pause and drop out of the game, resulting in the AI taking a hit. Keep repeating the process and you can force an easy win. Pun intended.
Switch Hitting
Freeplay (or Free Mode) is best for exploring previously cleared stages for studs and minikit parts. A preset "cast" is selected for a particular stage or mission which allows a player to access all the doors previously missed in Story Mode. Use the L or R keys to cycle through the cast while playing on free mode.