Battle command pointers and general question

The first place I'd look is C2/19EF and probably change that pointer to match Item (at C2/19C9). The same thing may need to be done at C2/279E. I don't believe anything would need to be done with D0 or D1.

You may also need to look at C2/04D2 if you want to keep muddled/charmed/coliseum auto-battling characters from using items.

As for Gau, you can just change the trigger for the event. Check the battle script for monster #370.