First off welcome!
If your vehicle is not lowered or doesn't have the ROW M030 option, then technically I guess you could put any spacer you want on. A spacer simply moves your wheel(s) out. If you go too far you might get rubbing w/ excessive vertical wheel travel though.....
I think the max lengths Porsche recommends for the 986 are 7mm front, 17mm rear which both keep the outside edge well inside the top of the wheel arch so no rubbing will occur.
With spacers you will need longer bolts (equal to the size of the spacer) if you go w/ the "sandwich" style, so count on $4-5 extra for each new wheel bolt. If you go 17mm or more, you most likely (for safety purposes) won't be able to go w/ the "sandwich" style but will instead need the kind that you will bolt to the rotor using your existing bolts and then will use lug nuts to attached your wheel to the spacer (which has stems).
What ever way you decide to go, if it's more than 5mm (which ain't much since 24.5mm = 1 inch), absolutely get hub-centric spacers (has lip to match up to rotor hat on inside & wheel on front side). If 15mm or over you might want to get the wheel balanced on the vehicle.
A lot of P-car owners go w/ H&R Wheel Spacers. Wheel Enhancements and Allsprings (just add .com for their websites) seem to be the major places to buy from too. Might search on either of those names to find out more answers too.
Hope this helps