I have designed this Portable Arduino Bot. This robot is small, compact, durable and fully equid with LEDs, switch, buzzer, etc. you can also equip the bot with the sensor that would work with your project. I also want to encourage kids to program and what is a better way to do so by infusing the project with the Star War themes.
Since you mentioned that it can be used further with additional sensors, as a portable testing platform or a piece of sci-fi, I would like to see for what purpose did you use it for.
You also mentioned one bot with sound option. Could we maybe see a video with sound, how is it working?