That's a fairly customized bit of wiring you're trying to implement. It may be helpful to find a local mechanic to help you with this. Some of us may be able to do it over the internet, but there's too much potential for miscommunication and bad implementation.
That being said, if you WERE to do it on your own, I'd take in small steps: one fix for the headlight, then hardwire the headlight into the ignition somehow. It should be easy enough to disable the starter portion by carefully disassembling the control section that has the starter switch and disconnect one of the wires to the switch. I'd leave it as close as possible in case you want to reconnect it.
Just my 2 cents worth.
Luke M
Used to have a 1979 CB750L, sold it as a parts bike, now riding a slightly modified 1984 VT700C. Network/Field Engineer. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.