I think legally you need headlight, tailight, and horn... maybe signals if the model year had them?
So not much wiring. A battery, fuse, keyswitch, wires from there to the regulator and ignition coils, and also to the lighting switches and horn switch. Plus to the horn and lights of course. Add a flasher and the extra wire for signals if you have them.
Charging is rather simple as well. Alternator wires to the reg/rect - one field wire gets grounded - and a wire to the battery +, as well ass the wire from the key switch.
There's a comic-book style wiring diagram for a minimal chopper harness that uses all the stock parts.