Not all of those things apply to the same type of UHC. (pvp or coop-enderdragon) That first list was mostly related to the PVP UHC, so I won’t address that if we’re going enderdragon.

The second list had some technical check lists for myself as well as some design challenges. The separate-inv and world border is a checklist. The visible border is an idea to improve it.

I wouldn’t allow any TP. People would have to walk/run/ride to each other.

Not all potions would be disabled, but regen potion is considered too easy once you get it. That’s why they disable or forbid it in the Mindcrack UHC events.

As far as a leaving penalty, I don’t know if I like losing all inventory after 30 min, but I’d have to give it some thought. It really depends on how long the UHC is planned to go. The penalty would need to be considerate of people’s time, but prevent people from exploiting difficult situations. If you’re surrounded by mobs and are going to die, it’s easy to just disconnect, and some people might not think anything of it in their panic.

Scoreboard was added in 1.5 and allows you to put information below player names, on a sidebar, or in the tab list. We use it in our many PVP games right now, and some other mini-games.