For your first question regarding "lubricating" versus "cleaning" the mating surfaces: I'm sure you're right. It was probably a bad translation of the manual to English that ended up instructing you to lubricate. However, it would be worth an e-mail to the gasket manufacturer to ask if the gasket should go on dry.
If your valve cover gasket is more than a few months old I would order one. They're about 7 bucks for aftermarket and $12 for German-made. If nothing else it is cheap insurance that your job will go smoothly.
I'm sure you've read about using real MBZ antifreeze. I just picked up some yesterday and it's not cheap ($12/gal), but my local parts wholesaler supports the claims made here on the board. He said that he used to recommend Prestone or anything with anti-corrosion additives and that MBZ antifreeze was a rip-off. Now he has been listening to the local mechanics who say they use MBZ antifreeze in Hondas, Toyotas, and everything else. It is just plain superior. They also claim that a car can run 10 degrees cooler with it. Okay it's all anecdotal evidence, but for a few extra bucks I'm giving it a shot.
This has been a great thread!
Experience is something you don't get until just after you need it.