Planning to 5box. Which toons to pick?

[Zub]

pally tank, ele shaman x2, boomkin(or resto druid), resto shaman(or 3rd ele shaman)

i kinda like having 5 different classes, and i've done 3 ele shamies before.
What exactly does 3elems or 2 elems/1boomkin bring that 1elem/1boomkin/1frostmage doesn't?
is it just to make things easier?

DON'T MAKE A MELEE GROUP

I see plenty of 5-paly or 5-DK groups working well, so i believe it's probably ok to do melees (even though probably less forgiving than range)
what do you warn against exactly?
in any case, this would be the second group, and not played nearly as much (and probably not before the first group gets to 80 and a few heroics )

Thanks for the feedback
-Zub