1990 Toyota Corolla headers and exhaust pipes

Is it right that I should use headers that the diameter is no more than the size of the exhaust manifolds, right?

and then should I use the same diameter size for the exhaust pipes? Or how bigger the exhaust pipe can be?

does a resonator add more back pressure? The setup is that the muffler can is setup as close as possible to the headers, and the resonator is welded almost one inch close to the muffler. Any idea on how it would affect engine performance?

thanks guys