Headers Time

I'm ordering some hooker competition headers from Summit for my dart. They include gaskets and bolts. I guess I also need to order reducers. Is that correct? Next question is do y'all suggest 2 1/2 inch exhaust or 3 inch? Question number 3. If I turn the exhaust down right before the rear axel im not gonna die of carbon monoxide poisoning am I? Or am I better off piping all the way back?
On dumping the exhaust: I dumped mine and it kicks dust up all over the car, so keeping it clean can be a chore. I don't really smell any exhaust fumes coming in the car while driving though. Could be different depending on the car. I'm not sure what your application is though. Maybe give some more details on power, intended purpose of the car, and what your setup is.