Yes, the CG is measured from the LE of the wing.

If you're just flying the plane for fun, it doesn't matter much if you can stop the engine from the radio or not. But, strictly speaking, contest rules usually require the ability to kill the engine from the TX.

I've heard that GMS considered the inability to kill the engine a "feature", but it just seems like sloppy tolerances to me.

You can often fix an engine that won't shut down by sealing up everything in sight with RTV silicone. Esp the backplate and carb.

But, if you're flying off grass, and you use the black MAS props, you can land with the engine running and not break the prop, I do it all the time. You just idle all the way down, and come in at a really flat angle, and slow the plane way way down before touchdown. You'll kick up a little grass, but you can do it with out breaking the prop.