People who are in it - is toxicity frequent in there? I don't want to join a server without being assured that it isn't a huge cesspit full of trolls, flamebaiters and people who break Discord's ToS by using it before they're 13yo.

What would be it's "hazard level" ranging from 0% to 200%?

I'd say the Subeta discord is a Hazard level .01%, to 1% at most. Everyone stays pretty cordial there as far as I've seen.