Whatever you choose, they should be NON-resistor plugs. Your car has resistance built into the plug caps. If you use a resistor plug, you will be doubling that value. There is still controversy out there on this but if you do it as MB designed, you can't go wrong. In my case, the only plug I could find locally was an NGK. Don't remember the designation but BP5ES rings a bell.

Your idle should be imperceptible. Mine was smooth as silk up to the day my wife totalled it. I was in the car with her and neither of us were hurt at all, a testament to the rugged safety of the car. Even our marriage survived the wreck but it was touch and go.

It was my daily drive and after initial sorting gave me 4 trouble-free years of service and pleasure. Follow others advice. Drive it for a while. You will probably change your mind about selling.