DisplayName max length? Docs for other details?

I've seen some pretty long display names. I doubt there is documentation on it. I recently had to ask support about the max characters in a text widget on a dashboard (it's 400KB btw). There wasn't any documentation on that either.

I'd hit up support to ask (and ask for documentation to be built). Alternatively, you can always test it out by modifying an existing device adding more and more to the name until it refuses.