This is a great Add-On. One suggestion for this would be to add this event.
RemoveRPGItem [ITEM] [AMOUNT]
I know that there is a RemoveRPGKeyItem of sorts, but that event (I think.) is for Quest Items. This event that I'm suggesting could be used for crafting or making potions. When you smith a weapon requiring 2 Iron Bars, for instance, SellRPGItem is not a smart choice due to the fact that it sells ALL of that specific item in the player's inventory. Also, it is illogical to sell the ores in this case because it will likely say "You sold 7 Iron Ore for 0 Gold". I'm thinking of making a 6-8 Player Dungeon RPG using this system for Skills and Items, but when I was getting to the crafting, this is where I ran into problems.