Please review my wiring plan

Bad conduction of contacts and wires that stop a function is way more common than shorts that smoke or blow fuse and even with a relay the horn is still too muffled. I would only use one fuse and just relay the head lights which do get detectably brighter and handle bar switches cooler. Chart implies a Negative Ground system with + polarity feed leads.

Grandpaul, what are the 2 heatsinked components in your photo? One I assume is the regulator/rectifier but how about the other one?

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.