I'd like to know if it's possible to add multiple tool types to a single item or increase the efficiency of a tool to a separate harvest material? such as making a Pickaxe better at chopping wood or giving the ability to till dirt with a Pickaxe.

In your code override the ItemTool Function

 

Set<String> getToolClasses(ItemStack stack)

 

The code checks every one of the string tool types in the list to determine if the tool is effective against that block.

Since hoes have their separate handler I think that hoe is not a valid tool type. You could have right click functionality though. (onItemRightClick...)