Hi,
Don't forget the amount of static electricity you will be producing.
One of our national supermarkets uses a kelly type pneumatic system, the pipes always look dirtry/grubby due to the static attraction of dust, each checkout point has a gnd wire from the pipe going "somewhere".
If you are pushing the "chase toy" through a decent sized pipe, you will need to check if you can supply the volume of air needed to push the full pipe length at the required pressure for the speed you want to try for.
You may need a large diameter "firing" valve and Accumulator to push the toy across.
Or a light weight tumbling "chase toy" such as a ball.
Tom.. 