Is it bad manner to have full Hell skill quests done on a lld(level 30)character?
What about level 9?

I was always under the impression that lld characters are supposed to be non titled (never killed Baal in normal) but some people are telling e otherwise.

No

You'll be at a big disadvantage if you don't get help rushed.

that was a thing briefly like 15 years ago

I only know of one person on east who still does that and he doesn't even duel