I have a set of Gemballa Competition 18's on my '01 Boxster. 8.5 x 18 fronts with a 46mm offset and 10 x 18 rears with a 40mm offset and they fit perfect with no spacers. They do push the outside of the wheel/tire flush with the outside of the body, but no rubbing whatsoever.
I would bolt them on your car first before ordering any spacers. I think you may be surprised at how well they fit.