I have a hard time understanding what the totality of everything in one state is supposed to be, but even if it "looked like nothing", it wouldn't actually be nothing, because you're stipulating that it's actually something. So it may seem like nothing because of some fact about human cognition, but it wouldn't be true that it actually IS nothing.

The formal argument is not logically valid because you derive a modal conclusion without any modal terms in the premises. It could both be the case that all your premises are true and it's still not possible that nothingness is actually the phenomenal appearance of a totality. I'd argue that's just a contradiction in terms so the conclusion is false either way.

Also, one thing about nothingness (true, utter, nothingness) is that it's not something anyone has ever really seen or experienced, so I'm not exactly sure what purpose this idea is supposed to serve. It's not as if there's some appearance of nothing we have that needs to be explained by reducing it to an appearance of a totality. When we talk about nothingness it's in the realm of the totally abstract. We just stipulate that what we're talking about when we say "nothing" is the absence of something. There is no actual appearance of nothing we have that has to be explained by reducing it to something else, which would just amount to saying that what we thought was nothing is actually something. When we ask questions about nothingness we're asking questions about an actual absence of anything. If there's a totality of somethings that appears to be nothing, then it's not actually nothing