How you wire the KILL switch depends upon what you are using for handlebar controls. If you are using the Motor M-switches, then the same button that you would wire to START and press once, you press twice to KILL the motor. This is a built-in feature of the M-Unit.
If you are using the stock controls, then you can wire a BLACK to RH STOP/RUN, then come off that with a BLK/WHT to the coils. This is exactly how the stock bike is wired. Moving the switch to STOP, severs power to the coils. Move it to RUN and you have 12v on BLK/WHT and the coils are powered.
As for deleting the starter motor, you don't gain much overall. You need to plug the case so oil doesn't leak out. You can delete the solenoid, and that eliminates the Y/R wire from START output, the Y/R to START input, and you run the RED wire from M-Unit power directly to the battery POS terminal.
The M-button is pointless. And it MUST be installed within steel bars to function properly. If you are using clip ons, they are made from aluminum and the M-Button will produce erroneous functions. It's far easier to wire your bike eliminating the M-Button by simply running the wires from your LH and RH bar directly to the input side of the M-Unit. These are purely "ground signals" that trigger that circuit. The output side runs directly to the component.
Another benefit of not using the M-Button is that you can simply move the wire at the M-Unit input side and change the behavior of that button. For instance, if you are using momentary switches, and decide that on your LH bar, you want a button to be HI/LO and you previously wired it for HORN, simply move the wire at the M-Unit. Now its function is different. Make that change with the M-Button, and you must cut the connection (2 wires) and re-solder it, shrink wrap it, and undo a fair bit of sheathing. Not worth the effort and you avoid any anomalies in function behavior.
Send it back. Trust me. I've only wired up dozens of these things and helped dozens more do the same. And there has not been a single person with an SOHC that has used the thing long term. In fact, I think I have 3 of them sitting on my parts shelves from folks abandoning them.