Clogged converter, running too rich or a misfiring plug.
Having no catalytic converter installed is illegal and can cause a myriad of problems. Probably not a backfire though.
Yes, internal coolant consumption can damage a catalytic converter.
No, the catalytic converter is downstream from the EGR valve so it has no effect on it.
No, the catalytic converter has nothing whatsoever to do with your defrost system.
A bad catalytic converter can cause hard starts if it has become clogged. This produces excessive back pressure in the engine.
yes it can
A bad coil can damage a converter. If the engine is misfiring, it will cause raw fuel to get into the converter and that can cause failure.
That depends on the engine and the fuel you've used. If the engine starts burning oil a catalytic converter can fail rapidly. Some fuel additives can also cause a catalytic converter to fail prematurely.
it is ok to continue driving the vehicle while the catalytic converter is not working properly?