One of the nifty things about WoW is you can do your macros in regular macros, or an addon like Gnome Sequencer, or via full-featured multiboxing tools like ISBoxer. The nifty thing about doing macros in ISBoxer is that you don't need to maintain all the macros across every toon every time you make a change. Just re-export, /console reloadui, and voila.

Jamba is an addon that provides a lot of "quality of life" improvements for multiboxers, such as automagically taking the same flight path, warning you when a follower breaks follow, selling the same piece of junk loot on all your toons at the same time, quest synchronization/monitoring, and a whole bunch more. It's not technically needed but it's a good way to get a lot of things done easier and without having to scrounge up mods and tweaks for all the various areas where multiboxing is tedious.