Custom bosses - Anything that makes leetx stand out from other servers is a great idea in my opinion, and custom bosses would be a great way to attract new players and in the future, possibly win back some old players.
Pk box - I think it may be a nice addition to the server, but to stop people from just using the pk box, maybe add some sort of con to it, such as only 2 pkp per kill.
Fishing guild - Maybe if the skills were spread out a bit (a mining area with a specific mining teleport for example) then it would be a nice idea. As it is though it wouldn't be much use, as you can fish at the general skilling area.
Super man armour - Superman armour would just be tacky and a waste of time. The time could be much better used by adding torva or another custom armour set or weapon.
Player list - Great idea! Maybe staff could have their rank next to their username in the players list, or even have a separate ::staff command to see all online staff.
Custom Claws - I completely agree that donators should be able to use custom weapons and armour. Whips, claws, godswords and chaotics would all make nice customs.
Owner cape - I think that all staff ranks (possibly including donators) should have an item that they can wear to show of their rank. It could also be useful for moderation purposes as well.
Donator codes - Codes like ::setskill and ::bank would make the game WAY too easy for donators and would be really unfair on people that either don't want to or can't donate.