I do kind of the same thing.... only i have it set up with the main guy being the focus target. I 5-box, and i have it set up so i don't have to switch between abilities when i switch mains. when one becomes the main, he clears his focus and the other guys all focus him.

the switching macros are very simple, but i have a different one for each toon:

/clearfocus
/focus <toon name>

and for the toon that is becoming the focus, just /clearfocus
these macros are bound to the same keys as my PiP-- Ctrl + Numpad 0, 1, 2, 4, 5 to switch

i have my spells set up something like this:

/assist [target=focus, exists]
/cast Lightning Bolt

^ this makes it so you can keep the macros on your bar even if you're soloing. only downside to all of this is if you want to use your focus for something else.

and following is easy too:

/stopmacro [target=focus, noexists]
/follow focus