Take a deep breath and relax.
The simple answer is, "follow the manual". Nothing you do during an oil change can't be undone. If you overfill the oil, you can always take some out. If you underfill, you can always add more. You will not hurt anything test riding your bike a quart low, then using the sight glass to determine the proper fill level.
BMW is maddeningly vague when it comes to viscosity. My manual lists 6 different ones for 3 different temperature minimums. What that says to me is that the Boxer isn't particularly picky when it comes to viscosity. I've got a bunch of 20W-50 gathering dust in the garage, so that's what'll be used at the first change. I've got 10W-40 I'll use in the winter. I may use Mobil1 15W-50 when I need to restock.
It's unfortunate that it's impossible to have a decent, educational oil thread. Between the people who insist you have to use the manufacturer's labeled stuff (even though no manufacturer makes their own oil), the Ams0il zombies, the dino/syn war, and the people who have nothing to add other than mocking the oil thread itself, it's impossible to get good information. Hence the reason I did the UOA on my last bike. I'm satisfied that motor oil is motor oil, and as long as the viscosity's in the right range, the factory change interval is adhered to for warranty purposes (because oil will go much, much longer), the API grade is correct, and the fill level is in the right ballpark, my engines will never suffer from any oil-related failure.
As for everything else, you need to remember that you're on an internet forum, you're not talking to BMW engineers. No vehicle forum is immune to Internet Hysteria, and this one is no exception. People like to bitch about things, especially when the bitching is free and anonymous. While the internet has probably helped get a few legitimate issues rectified, by-and-large, people worry about nothing, To read the forums, you'd think that every vehicle on the road was a few short miles away from violently self-destructing. It ain't so. Print yourself out a factory maintenance schedule and follow it. That's all you need to do. If something breaks, fix it. Go ride. Lather, rinse, repeat. It's not rocket science, no matter what some people may lead you to believe.
As far as the language thing......You live in North America, as do the majority of other people on the various BMW forums. Our passengers aren't pillions, the black things on our rims are tires, and we throw our stuff into saddlebags. The North Americans who insist on using the overseas terms are trying to live the lifestyle....It doesn't do any harm, so I let it go with a smile.