Three existing accounts, call them A, B and C.
Two new accounts, which will be RAF referred from B and C.
Two new accounts, are D and E.
Your set up will be:

A
B -- RAF Linked to -- D
C -- RAF Linked to -- E

A is the boosting account, with the 80's on it.

For the boosting, I would boost with your highest level (and best geared if similar level) tank type.
If all else is equal, a Feral Druid is the top choice, but a Prot Paladin is a close second.
Any tank type works good.
Or lacking all of these, any high level works, with AoE classes higher then not AoE.

During RAF, you'll want to boost a lot of toons on BCDE.
You will want to end up with a tank option on each account.
And a healer option on each account.
Which opens doors, for later teams.

You might want to go 4x class, for a few types.
Like 4x Shaman, 4x Druid, 4x Warlock, 4x Mage, 4x Rogue, 4x Paladin..
Whatever sounds like fun playing, with one other class as support.

A mixed team or two, might be fun to play as well.
For the RAF, I'd try to "boost" them as 4x one class.
It just makes it easier on you, for training and such.
You don't need to play them 60-80, as 4x one class, but you can.

From a boxing point of view, a Prot Paladin is the best tank by a long shot.
They tank well, and macro much easier then anything else.
For this reason, a DK tank is the worst, but most will "drive" from the tanks window, so a DK will work.

The top healers for teams, are usually Disc Priest > Resto Druid > Holy Priest > Shaman > Paladin.
I'd only really look at a shaman, as healer if you otherwise lack shammies on the team.
Bloodlust/Heroism and Totems are huge, and without these in the DPS, Resto is probably top choice for heals.
For a melee composition, Resto Druid and Resto Shaman are very attractive, for the ranged AoE heal.
A Paladin (and shammy) lack mobility while healing, and the Pally lacks AoE heals too.

In a 3x/4x Druid/Priest/Shaman team, you can choose for your DPS toons to cover both DPS and Heals.
For example 1x Tank + 4x Shaman, do not need a dedicated healer, as the shammies can cover both roles.

I'd get a bunch of things to 60th, during RAF.
And then worry about 60-80 afterwards.
Boosting will be the fastest leveling.
01 to 10 - Group all five and quest; destroy stuff with the booster.
11 to 20 - (Horde) Shadow Fang Keep or Wailing Caverns.
11 to 16 - (Alliance) Deadmines.
16 to 20 - (Alliance) Stockades.
20 to 45 - Scarlet Monastery
45 to 55 - Stratholme (the door you need a key to open).
55 to 60 - Hellfire Ramparts.
60 to 65 - Underbog.
65 to 68 - Auchendoun instance of choice or CoT Old Hillsbrad.

68+ Northrend.
Do both: Howling Fjord and Borean Tundra.
Then do both of: Grizzly Hills and Dragonblight.

You can mix instances as a team (Tank, Heals, DPS) to supplement leveling.
And queue for AV too.