This answers your question about availability & prices for sparkplugs.
http://catalog.eautopartscatalog.com/mercedesshop/sophio/quote.jsp?clientid=catalog.mercedesshop&cookieid=1FU1CD1PL1J80QTB0R&baseurl=http://catalog.peachparts.com/&partner=mercedesshop&year=1998&product=F1000-116348&application=000346404
Can't help you much with the rest.

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2007 C 230 Sport.