I'm not surprised you are finding them difficult, to be honest I think he must have been having a "Coleridge moment" while writing those lines!
This is my understanding of them, but I expect you may get quite a few interpretations given their impenetrability.
Levity: Humor or frivolity, especially the treatment of a serious matter with humor or in a manner lacking due respect.
To me it also conjures up the meaning "light", as in "not heavy", hence "jovial" or "light hearted", almost "bouncing with joy".
Hugeness: Enormousness (this word is reasonably straightforward, but hugeness usually also conveys the idea of weight and heaviness).
Maenad: One of the "female followers of Dionysus" and "Their name literally translates as "raving ones."".
suffix "-ism": Denoting a system, principle, or ideological movement.
Mass: (In general use) weight. [or bulk, my addition].
In general I get the idea that he is saying that the mansion is a huge thing; and huge things like mansions are usually static, hence the additional imagery concerning movement to indicate the storm's violent power and its effects. His imagery is also creatively contrasting lightness with heaviness and seriousness with joviality. In simple terms it is the mansion being destroyed by the storm, but the language he employs provides a far greater intensity than those simple words. All of these ideas combine to generate the sense of something being whisked up into a frenzy, leading inexorably to its own destruction.
Moving specifically back to the lines in question:
"It was the levity of hugeness! it was the mænadism of mass!"
My interpretation is:
"It was the embodiment of bouncing hugeness! It was the epitome of manic bulk in motion!"
That is about as near as I can get to the spirit and meaning of these phrases.
Interested in Language