Please review my wiring plan

One of the most important things to do is run earth wires to all lights etc. I run heavier wiring [ including earth ] to the head lamp, and also run the head lamp through relays. The relays will give you a really bright light because of negligible voltage drop, which you would get through your switching. I also agree with running separate wiring sets rather than one loom, but you can cable tie them together to make it neat. Put a horn in place, and find somewhere else to fit the horn/s. we have to have horns in NZ, and the last new one I fitted about three years ago sounded like shit the other day so out it goes while I have the rear wheel off.