I don't have highway stats but around town I'd say I get as good or better mileage as I did with a single carb (850DP), normally aspirated BB. Crack the throttle and you're moving. Really depends on how heavy your right foot is.
Run the headers you want that will fit. The blower will definitely generate more under hood heat. I run a heat shield under my master cylinder. My floor boards get pretty warm. No problems though.