Electronic ignition for stovetop - insulation?

For the stove top: You don't need to install new electrodes. Just connect the new piezo to the existing electrodes and it will work fine.
In fact if your knob part was still working you could hook both it and the new sparker to the existing electrodes - like I did.

I haven't done the oven but I think the wire and electrode you bought will be fine since it's in a hot area with a BBQ too.