While I can't write in German, I can attempt to get you some useful information.
Games like Street Fighter 2 use a 3x2 arrangement like this:
However, Neo Geo games use a four button arrangement like one of these two:
- or -
This leads to a general concept that a typical "best compromise" is a 4x2 arrangement like:
This lets you have buttons in good places for most any game.
As for why the one button seems offcenter on the one cabinet you linked, look at this image and think about how your right hand fits over the buttons:
You'll notice that the first finger is a bit shorter, so actually bringing the button down a hair makes it a bit more comfortable for some people. Thus:
As for why the third joystick, there's about a 99.9% chance that that third stick is a four-way joystick. Games like Mortal Kombat, Street Fighter 2, Gradius, and so forth are fine with 8-way sticks and in fact DEMAND them. That's a large chunk of the collection.
However, there are a number of games that used four-way sticks in the arcade. These games react in unpredictable and potentially frustrating ways when a diagonal is hit on an 8-way stick. Games in this category include Donkey Kong, Pac-Man, and Dig Dug as examples.
You asked if games have multiple wheels or spinners? The answer is yes. Some racing games (Pole Position) used spinners instead of wheels, firstly. Now take a look at this photo of Super Sprint: http://www.premier-md.com/images/Arcade/Super%20Sprint/SuperSprint_Front_1.JPG
That'd be three spinners.
Additionally, you may want more buttons to actually control your front end beyond simple coin-up. You may want volume adjustments, MAME slider control, game selection buttons, exit (you may wish to protect this from accidental press!) and so on.
I can't speak much to your video choices, though, maybe someone else here could help. I hope this helps you.
Try checking the MAME manual at http://docs.mamedev.org