I think the important thing to remember is that you have two columns of keybindings in wow.

So both characters might have [`] to [backspace] bound to the same 'basic' things (so for example [1] bound to 'lets frost bolt the same guy') On a very basic setup it might look like this: MageA this is "/cast frost bolt" and MageB "/cast [target=focustarget] fost bolt".

On both characters you might have [F] set to "follow me" which on MageA would be set to "unbound" (and thus ignored) and MageB this would be set to "/follow focus".

Writing some lua that redirects Error Panels to your main characters chat panel from the slaves comes in handy (to capture bad facing, no mana, cannopt do that yet, etc).