Wheel spacer question

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I'm thinking of getting wheel spacers but have several questions. Seen Stryker's Boxster with 5MM and he has 18" wheels - very nice by the way!

1) What are the advantages/disadvantages of wheels spacers?

2) Are they easy to install without taking it to a pro and how long will it take?

3) What should I look out for when I install them?

4) My 2000 Boxster S has the 17" classic sport wheels. Can you make a recommendation on the spacer widths for front and rear wheels without rubbing?

5) I think Porsche, H&R and Eibach sells wheel spacers. Who would you recommend and where????

Much thanks in advance!