Well - I hate to discourage anyone, but if you’ve never done this before (or similar things with electronics, using a soldering iron, understanding LEDs & power requirements, electronic schmatics, etc.) - you could end up with a rather expensive bummer if you blow out an LED or accidentally fry a board.
If you aren’t experienced, I would suggest buying a basic looking saber with sound installed that you can then customize the external look of to your heart’s content - and learn a lot more about the components and work your way up to doing the electronics as well.
(I am saying this as someone who has accidentally both blown an LED and accidentally shorted a sound board years ago before I really knew what the heck I was doing
)