Danger level isn't that big of a deal from my experience, as you generally have good enough gear to deal with the stuff unless you're using like Armor of Great Health +absurd. This is especially the case with weapons, as they generally don't bump your danger level that high compared to the benefits. Regarding Vermis, dump it IMO. It's horrendously annoying to have your opponents get teleported away when you're trying to kill them, which becomes more and more of a problem when you start encountering tougher to kill opponents.

1. Again, don't mind the danger level. Dragon hide is much better than phoenix feather for armor, and not just because PF melts really quickly in any kind of acid.

2. The only other way to harden stuff is praying. And no, you can't harden past dragon hide as there's nothing left to harden into.

3. Yes, applying the 1-shot wands is generally a good idea unless you really want to have that emergency clone of something for some reason.

4. Elpuri's bite damages stuff in your inventory as well as the things on you, which generally means your wands are going to blow up unless they're in boxes. It's not unheard of to have them explode even inside the boxes. This also means you don't want to have any bottles of liquid in your inventory when you take a hit. Unbreakable source of light is a good thing to have as well.

5. No, there isn't. Drinking from wells can spawn mommo slimes or brown slimes, but that's out of question since we're talking about GC9 which has no wells.

6.