I'm afraid im not quite sure what you are asking here...

what should your interface look like when multiboxing? what mods to use? what macros to use?

I believe its all presonal preference. I use multibox v2 to track my characters, I use pibull for unitrframes and bartender for bar replacements, and about 40 other addons for all kinds of other stuffs... is that what you are interested in?