Yes, if it just started in time you will lose power and speed, replace it, it is breaking up inside.
It could. One, it is illegal. Two, the computer may try to adjust for the missing catalytic converter and that can cause poor economy and drive ability.
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.
Yes
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.
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.
yes it can
No
Yes
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.