currently it sounds like a fairly large bit of effort to add capabilities for everything
if you were more specific, it would narrow the scope a ton
i tried to be extremely specific but the basis is this.
there will be 20+ that all can be customized in a menu in the server settings.
the items can change the playertype the player is, their weapons, and their health. the items they had beforehand will be gone as well as the ultimate item while it is in effect.
once the ultimate wears off the items they had beforehand will be restored, their playertype, as well as the ultimate item itself.
once the ultimate activates the charge meter will be reset. the meter will be displayed on bottomprint when the item is held and when it fills up it will notify the player via a message in chat.
these items will be invisible when held, and when clicked after being charged up after doing a certain amount of damage/healing (this amount will be set by the customize menu) will activate the ultimate.
the ultimates can be changed respectively via the menu. each one will have its own page in the menu with the details that can be changed like how long it lasts, or the playertype the player has while it activates, or what weapons it has, etc. it can use any weapon or playertype the player has in their server.
the host will be able to decide who can edit them or not, but by the very minimum only admins can.