To hookup your separate switches, you can connect as follows:
Engine Start - White/Black connects to Red using a normally open push button
Engine Kill - Yellow/White connects to Yellow/Green using a normally open push button
These are the wires in the connector/plug for the multifunction switch.
If you want to operate lights, add the following:
Low Beam - Yellow to White
High Beam - Yellow to Blue
A single pole three position toggle switch with center off will be fine. Yellow goes to the common terminal.