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?