Less fighting please people. This is one of the reason hosting pvp-related event is "icky" :\
-Potion skills from chemist, allow or disallow or limit it?
I'm with the limit option. However trying to count the number of potion thrown during a fight is tedious, a number of potion for the whole event should be set, and that will depend on each event. Could be a generic number of potion/slim, example if the allowed number is 30, then the chemist can decide to have example 10 slim red (for lif), 15 white and 5 blue.
-movement speed buffing items, allow or disallow?
I say no to "portable aco" buffing items.
-spell scrolls?
I'd say no as well, classes should use their own skills, or those obtained via gears.