Wiring and electrical is generally covered in most books on bales or natural building. This is really going to be up to your local codes and restrictions that might be imposed on your build. I've heard of building inspectors demanding wiring be placed inside conduit to prevent potential fires. If this isn't an issue I suggest you just run the wiring directly on the outside of your bales and plaster over them while finishing. Make sure you draw a detailed map of where these wires are though, if you need to change something in the future it is best to have a reference instead of punching holes in the wall.
On my cob house I just rigged the wiring with staples right onto the cob and plastered over them, I've seen others take a circular saw to create a groove to lay wires in instead. Check with others in your area who have done bale buildings and see what they have done.
Typically UF (underground feeder, rated for direct burial in dirt, unlike NM Romex) is allowed directly under an earthen plaster. Any plaster with calcium (Portland, mag, lime, gypsum) will eat through and dissolve that insulation/sheathing. To cover their liability, our local inspectors require that a little plastic gets wrapped over UF in case someone adds one of these calcium materials to their plaster mix. Bale pin (sod staple) the cable tight. We cut out our recesses with a Lancelot wheel on a 4.5" angle grinder. I think it's the quickest and safest way to cut and shave bales
I'd recommend trying to locate your breaker panel on an interior framed wall for both organization and future modifications.