[EDIT]Too slow... jluciani beat me :
There are some things to concider.
Are the leds gonna be individually controlled? (those within the cocoons)
Are the leds multicolored?
What kind of sounds are you aiming to make? Those of a piezo summer, or a regular speaker?
If the installation is goining to follow a predefined pattern, there is actually no need for the arduinos to be connected to the computer.
YOu can program the pattern into the arduino itself.