We're also looking for people to play/produce Chewie and Artoo as characters.

Each sound those characters make would be a numbered cue in the script. The producer for that character would find the right sound effect for that line to create the character. Example:

SFX   A distant rumble/explosion sound.

77. CHEWIE               (Surprised Growl)

78. HAN            Calm down. They’re just blasting more space in the ice to park more ships.

79. CHEWIE               (Growls question)

80. HAN How should I know?