for offset, you don't want to go more than whats stock, because when you push the rim further out past the pivot axis, this puts more force on the wheel bearings and steering box, not a good thing for longevity. this is why wheel spacers are not a good idea for our car, it's not exactly heavy duty suspension. also slows down your response time when turning the wheels

I wouldn't recommend anything over 19", in fact your better off going to a 18" rim on all four corners for a performance stand point, those big wagon wheels will suck hp, and the tires are ver pricey at 19 and 20"