The catalytic converter.
Yes.
It will use more fuel if you remove the catalytic converter.
YesYes
You will have to replace it.
If the vehicle came from the factory with a catalytic converter is illegal to remove it. It will also not run properly without the catalytic converter install.
Yes, it is a fedral law that all vehicles built with a catalytic converter have one in working condition.
Right after the catalytic converter or " downstream " of the converter.
No.
It is in front of the catalytic converter.
Yes
It is in the exhaust pipe, next to the transmission.