That diagram is useful, but assumes a lot.
What components do you want to keep? The stock switchpods? The stock reg/rect? The horn?
What you need depends on these choices, but:
You need a battery.
You need a fuse.
You need an ignition on/off switch, usually a key switch is used.
You need a momentary starter switch, and the stock solenoid relay for the starter motor. You can use an automotive key switch with the starter function for both ignition and start.
You need a headlight dimmer switch.
You need a brake light switch, and should have one on both front and back brake although back only is usually acceptable.
You should have a horn and horn switch.
The diagram shows all of this, but the "ACC" and "IGN" terminals are confusing. Automotive switches have these, and you can put the lighting on "ACC" so you can have them on without ignition on, but I don't know why that would be useful. Bike switches do not have this, Honda bike key switches usually have a complicated switching system for "parking lights" but you can ignore this and just wire everything to the IGN terminal and not have the "park" position do anything.
The rectifier output and the starter motor connect directly to battery "+", everything else must be fused. The fuse should be as close to the battery as possible to help avoid unfused wiring that can have its insulation rub through and cause serious damage when the wire melts or bursts into flame.
The fused power goes to the ignition switch, the switch output powers everything other than the starter motor.
The horn shown is powered all the time with its ground switched. I prefer to switch the power if possible, powered stuff corrodes faster than unpowered.
I hope you get it working!
