I'm totally with you Thomas. I too started day 1 and have actually quit several times because the endgame just fails for my lifestyle/schedule. Multiboxing though I think has me here to stay (or at least until the next big thing, hello is anyone else even trying to compete anymore?).

You'll definitely have more of a challenge doing 5 mans with 5 different classes than those of us who do 2-3 classes but there are many success stories on the forums. Like Opt said, mainly try to stick to 4 casters and 1 melee because of the movement issues. Given this I'd shelve your warrior and rogue for sure. Most everyone (sans Suvega a few others) whole-heartedly agree that Druids and Pallies make better MB tanks because of less micro management and better group aggro. You're going to have PLENTY going on with the other 4 so keep your tanking as simple as possible.

Healing I'd go with Priest/Shaman/Druid rather than Pally. Why? Because when you don't need the big heals they can participate in DPS easier than the Pally. I'd really lean towards the Priest for healing re: best group heals + all the rez you can eat.

DPS I'd sacrifice the uber dmg of Hunters for the CC, buffs, etc. of Mage/Warlock/Shaman (totems pwn, particularly grounding totem). For these you can setup a pretty simple cast sequence for each and get them down to one button for general dps. Something like

mage = scorch,scorch,scorch,fireball, fireball, fireball...
warlock = curse1,curse2,curse3,shadow bolt, shadow bolt, shadow bolt...
shaman = lightning bolt (lol)

I think most people do variations on these such that like button 1 is for non elites (curses wasted, just direct fire), 2 is for elites, 3 is for bosses, etc.

So in summary, this is how I'd do it

Priest - HEALS
Mage - DPS1 (CC)
Warlock - DPS2 (situational CC)
Shaman - DPS3
Paladin - TANK
Warrior - shelve
Rogue - shelve
Hunter - shelve
Druid - shelve

The heroics are definitely do-able and we've got many success stories on here. I think there are some heroics that may very well never be 5 boxed but we'll see. Personally I'm keeping my eye on Skarlot as he's got a pretty definitive goal of clearing all heroics (and uses a Warrior tank so lol @ my suggestions ).

GL and HF man!