You may have tripped over the different meanings of “artist” (e.g. English) and “Artist”.
In German, the word for anyone expressing themselves through or creating art is “Künstler“ (as art = Kunst).
An Artist ist an artist using his body, e.g. an acrobat. (So Artist is a subset of Künstler.) A second meaning of Artist, especially in compound nouns, is „a ...
Künstler := Artist, one who uses imagination to create aesthetics.
Artist := Performer, esp. in a circus; Artisan, one who is skilled at a craft.
The passage describes Nietzsche as being both able to create vivid scenes with words (the first sense, Künstler), as well as expressing those well and concisely (the second sense, Artist, like a wordsmith).
"Jemanden früher gehen lassen" is indeed an idiomatic expression in German language.
It is implied that the time you leave is earlier than the time you were supposed to leave.
You usually work till 5pm? - Ok but today you are leaving earlier...
»ans Glas klopfen« and »gegen ein Glas klopfen« can describe two different things.
The second one, which you encountered in the movie, is correct here, because in Germany people typically tap their spoon against a glass at larger gatherings to attract attention, e.g. if they want to give a short speech or if they want the wedding couple to kiss (in this case ...
Gegen in general means a direction (like towards), while an strongly indicates a contact/touch.
An example for this general meaning is:
Die Fenster gehen gegen Osten
In your special case there would be no knocking noise in case you stopped earlier, so it is pretty clear, that gegen here also includes contact (like against).
This is confirmed by DWDS, ...