I went with nec because I liked the sound better with one syllable. Neque would work as well (as I understand it, the only difference is that neque slightly stresses that it is a conjuction).

As for modo/sola, I had sola but then changed it...both translations share the same issue, which is that the original English "only nothingness" doesn't quite work for me. "Only", to me, suggests that there's at least something. What do you think of the following sentences?

• I listened at the window, but heard only nothing outside.
• There were only zero eggs left in the carton.

My opinion is that those are ill-formed in the same way as "Only nothingness above"; all three would be better off without "only". Similarly, neither modo nor sola seem right when applied to nihilitas, and for the same reason: the nothingness isn't alone, it just...isn't. I guess my real suggestion here is to modify the English.

Thank you for making me do the research on the phonetics. I reached for a term that meant "that sound that a g makes when it's right before an n", and incorrectly came up with "glottal stop". Now I know that it's a "velar nasal", so I learned something today!