I can't see wiring a car from scratch to be that difficult. Altering or adding wiring on some unibody EFI car from the past 20 years is a pain in the ass.
No, it's not very difficult at all. The hardest part is putting bundles of wire in locations that don't get too hot and protect them from abrasion, and making it look good. Plenty of room behind the dash for the puse panel and wiring, but I'm holding myself to a pretty high standard and want it to be well laid out, organized, and look good too(even if it's hiden from view).
Pretty basic stuff here: Headlights, tail lights, brake lights, blinkers, horn and guages. Throw in the heavier ignition, alternator, and battery stuff and that's it. I'm skipping the heater, electric windshield wipers (will use mechanical "clip on" for inspection), and stereo. The only comfort item I'm going with is heated seats.