[Perfectlap]

Depends on the roads you drive. And the weight of your wheels. I would keep the wheels small and light. But you can actually have an 18" wheel that rides smoother than 10# heavier 17" wheel. Try to stay under 18-20 pounds either way. OZ have some good options as far as weight/durability for a not obscene price, not sure about size though even 18" aftermarket wheels are tough to find. And replace the shocks, with your mileage you'll burn up whatever is left on a used Porsche of moderately mileage quickly. A new set of shocks will make the car feel factory fresh. It's probably the one thing 986/996 owners put off longer than they should. Probably because once you get in there it can get very expensive if more things need replacing.

p.s.
replace the IMS and water pump if you plan a lot mileage with that 2004.