1998 mustang v6 converting to dual exhaust

I have a manual 1998 v6 and I'm going to convert it to a dual exhaust. Does anyone know if this will hurt the performance of the engine, hurt gas mileage, possibly damage the engine, and any other possible issues. I'm putting a catted x-mid pipe thats 2.5" in diameter that's made by pypes. The catback I'm putting on is the flowmaster american thunder with super 44 series mufflers. Any information will be great.