Another easy level is the first one of Episode 1: A phantom menace, called: A bigger fish.
Just shoot the rockets to left & right besides the fishes. Minikits appear in bubbles. Very easy to hit. Maybe retry once more & the Minikits are yours.
When u got all the Minikits, it's a good level to farm studs, because the level is quite short & u get a lot of studs in replacement of the kits.