Nice idea but why do want to just stun your victim would prefer red led's, lets at least try to kill the rebel scum, even if we can't hit the side of a barn LOL .
I use the soundboards from small cheap toy guns, normally around $6.00 and the board is only 1" x 1/2", the speakers are small enough to fit in e-11 pipes and they come with a vibration motor which give the realistic feel when you fire the gun.
I did a similar thing to your idea in my DLT-19 build, managed to fix everything into the side cover box.