2. How to narrow my faculty of expression down to a moderate amount of simplicity?
You said yourself that you learned this way, and this sentence is a good example. While grammatically correct, it sounds awkward to my ears, even a little like legalese or bureaucratic language. I would express the same thought this way:
2. How can I learn to express myself more simply?
One way to do this is to read things that use simple language. I don't mean childish, I mean non-academic.
An excellent resource, I find, are Bande Dessines (not sure what they're called in German) like Tin-Tin, and Asterix & Obelix. Of course, the originals are French, but the translations into English are excellent. Unlike a childish comic (like Donald Duck or similar) reading Asterix will not bore you, and you will learn some street language, some slang, and a good deal of word play.
In order to learn to write in English this way, I would give you this task: also buy a copy of some Asterix in German (or French) which you have not seen in English before. Now sit down, and try to write down the translation. This will give you great practice in expressing yourself simply, because the version you're reading is simple, and you'll know in advance that a complicated expression just wouldn't fit the style, so you'll be forced to look for a simple solution.
Finally, get yourself a copy of the English translation as well, and compare what you wrote with the professional translation. This should give you some great practice.