Chris,
I have never used a 'kill switch' before.
That being said this is how I set up mine:
TX stick at full throttle=carb open full-without binding the servo.
TX stick and trim tab all the way down=carb fully closed-without binding the servo.
Idle is then attained by use of the trim tab.

I guess you might say I use my trim tab as a 'kill switch.'

The needle valve/spraybar assembly should be perpendicular to the crankshaft.
Adjustments can be made by increasing/decreasing the pushrod length and/or the servo arm attachment point.
Adjustments can also be made to the servo endpoints via the TX.

Getting some first-hand experienced help would be a very good idea. (Having someone with experience actually look/help you with the installation.)

Good Luck,
Jeff