Help me piece together a Heroic team

So I'm 5-boxing and have several toons in the 70 - 80 range, but my one full team that is 80 (DK + 4 Ret Pallys) just isn't cutting it for instancing at the moment. I'd like some help in reviewing the toons I have available to see what I might do with transfers and/or respecs to put together a group I can hit Heroics with and actually start to gear up more.

Account 1
80 DK (Def capped with partial Naxx gear), 80 Shaman (limited PvP geared), 80 Mage (partially Naxx 25 geared), 70 Priest, 71 Paladin

Account 2
80 Shaman (limited PvP geared), 80 Ret Paladin (partially PvP geared, full trinket/ring sets from Brewfest/Hallow'sEnd), 70 Mage

Account 3
80 Shaman (limited PvP geared), 80 Ret Paladin (partially PvP geared, full trinket/ring sets from Brewfest/Hallow'sEnd), 70 Mage

Account 4
80 Ret Paladin (partially PvP geared, full trinket/ring sets from Brewfest/Hallow'sEnd), 70 Mage

Account 5
80 Ret Paladin (partially PvP geared, full trinket/ring sets from Brewfest/Hallow'sEnd, assorted spellpower plate), 71 Shaman (near capped Grand Master Engineer), 70 Mage

What I think I would do is go from melée to caster.
Keep dk as tank.
Use a shaman on accounts 2 & 3.
Use Mage on 4.
Transfer priest to account 5 for heals.
An alternative without transfering would be use Mage on 5 and make one shaman a healer.
It's hard to beat priest healer though.
Just my quick thoughts on it.

Here's a possibility without leveling:

acct 5 - respec pally to prot to tank
acct 4 - respec pally to holy to heal
acct 1 - mage to dps
acct 2-3 shaman dps

That's something I would try out but I'm partial to tank+caster teams.

As far as heroics go, any tank can heal, but the Prot Paladin is much easier to run.

You will want your heroic team to include the toons you want to gear.
Badges can get you PvE or PvP gear, and if you want to gear a DK then the DK should be in the team.
If you're happy to build the best PvE team, and go with that as is, then the ranged team is easier.

Priest is probably the top pick for a healer, especially with a shaman already on the team.
I'd probably take a shammy healer over a priest, if the team did not already have at least one shaman.
With two elemental shaman, the priest will be a far easier option to heal a team with.

So you have Prot Paladin, Disc (or Holy) Priest to heal, 2x Elemental Shaman.
I'd think the perfect last addition would be either another Elemental Shaman or a Warlock.
Boomkin works too, but then you need to manage eclipse procs for good dps.
The Shaman is easier, you already have 2x.
The warlock gets you the 13% spell power boost, and can be /Click dps like the Shaman.
The druid also gets the 13%, but you need to manage Eclipse procs to match Shaman/Warlock dps.
The mage isn't a bad choice, I'd go with arcane for now; in 3.3, frost gets a persistent pet which should help the spec a lot.
At the moment arcane can just spam Arcane Blast, but a rotation of 4x Arcane Blast and 1x Arcane Missiles is better.
The frost spec is Frostbolt spam, with the water elemental on every cooldown.