...wow. If that macro was too hard I fear you may have quite a difficult time succeeding at multiboxing. Even with only one class I use:

#showtooltip /cast [target=focustargettarget,help,nodead,exists] Healing Wave; [target=focustarget,help,nodead,exists] Healing Wave; [target=player] Healing Wave

The only way to be completely efficient at multiboxing you're going to need some macros that extend beyond /cast fireball.