okay, this is coming from a guy who got his PC a month ago.. and read hundreds of threads of archives.
Im going to keep it simple and This is what i recommend:
-3M PII Fine Cut for the really messed up part of the car (heavy water spots, etc) - just don't breath the carniogenic dust! Great product, can easily remove most nasty things without wasting much time.
-Mothers Power Polish - Okay, i've tried Sonus SFX1, 2, and 3, Meguiars #9, Meguiars DC steps 1 and 2: this is the best one i have used. Unlike most polishes, you don't have to remove it before it dries. You can wait till it dries and then remove (so u don't have to put down your PC after each panel, saves time). MPP is aggressive on a cutting pad and easy on a polishing pad. It's EASY to remove. It's available over the counter. Leaves a beautiful finish. Since it's a cleaner/polish and it alters it's aggressive according to the pad, this is an extremely versatile product.
-Klasse All-in-one: an excellent cleaner/polish/sealant. It will lay down a nice clean layer that your LSP can bond to. Also leaves behind a pretty good acrylic protection. Easy to use. Goes on and off easy.
-NXT or Mothers Reflections. I personally use NXT right now, but i'm looking to buy reflections. Everybody that i know that have used both prefers Reflections more, supposedly more durablity and even easier to come off. Reflections is supposed to have a deeper carnauba look (better for black cars) vs NXT's rich shiny look. #26 would do good here too.
Well.. there you have it. Most of this stuff you can get at local store like PepBoys except for the Klasse, which you might have to buy online or at a Mercedes-Benz dealer.