You don't want an orbital sander anywhere near that IMHO. Something like this is much cheaper and gentler.

https://www.harborfreight.com/07-amp...hoCKhEQAvD_BwE

I just put the approach to getting the electronics into the holes on my build diary:

https://www.buildyourownguitar.com.a...t=5339&page=18

Not perfect, but the best way I have found.

Hang in there. Let it get good and hard before you start the final sanding.

I have a bass that uses the wring similar to what I think you'll be doing. I cannibalized an old guitar cable since you really only need to run ground and hot wires between the components. It has the benefit of being a bit stiffer than ordinary wire and is shielded. That bass has bigger F-holes than the one in my build diary. Hopefully yours will as well. It's nice when you can get some help from your fingers. Mine were mostly too fat to fit inside my super slender F-holes.