Just a few hints as nobody else has answered yet:
There is one misunderstanding:
Jenseits dieser Mittel ist der Mensch, ist der Künstler nur ein mehr oder weniger großes oder kleines Gefäß, das gefüllt wird von dem, der darüber steht. In einer fernöstlichen Weisheit heißt es: "Kunst hat nicht den Körper darzustellen, sondern die Kräfte, die den Körper geschaffen haben."
" the artist is only a more or less large or small vessel that is filled by what he stands on top of. A wise saying from the Far East goes: "What art has to depict isn't the body but rather the forces that created the body.""
I'd go for "a vessel, smaller or larger, that is filled..." (the German is inaccurate here, "mehr oder weniger groß" or "großes oder kleines", but not both), and now: not "what he stands on top of" but the other way round: by what is greater than itself (or superior to it, or above it; some godlike entity -- von DEM, DER -- is evoked). No matter what you choose, the direction of divine inspiration (filling the vessel) is crucial.
The first sentence makes sense to me and you got it very well, considering that it doesn't make sense to you (-:
But it's rather "pictorial shapings (?) of surface and space" (if you know what I mean) than pictorial compositions on a surface and in space; "Fassungen" equals "Gestaltungen" in this context. And maybe "impose no claims" is too strong, it's rather, "they don't presume", they don't assume or raise any claims.
And: The fragmentary is the artist's creative information about his expertise and his possibilities should be "The fragmentary is/contains/provides the artist's exhaustive information regarding his etc.". If the English is not clear: The state of the work of art as a fragment supplies all the information you will need (and get) regarding his competence and the possibilities at his disposal. (Having said this, I'd really go for competence and add "at his disposal".)
Maybe these snippets can give you a few ideas for tomorrow when you look over your text with a clear mind.
I guess, some typos (Gourcemar for Yourcenar and the like) are copying errors only?
And, if you have a chance and the German paper is not yet published, please draw the editor's attention to misleading errors such as "Kraft" for the preposition "kraft" or "Traum geboren" for "traumgeboren". Or the one I mentioned above. If you still have some energy left to do so.
Don't be discouraged, you did a good job. (And the German is rather elegant but, alas, not simple. Not the usual untranslatable rant, it's meaningful.) Best of luck to you!