I would go with a chain, A -- B -- C -- D.
Level a Prot-Paladin or Feral-Druid on A, with whatever you want on B-C-D.

Once you get the team to 60th, run most of the Hellfire quests.
The focus here is gearing the toon on Account A a bit.
Burning Crusade gear is far and away better then old world gear.

Then take your 60/61 tanking toon on A.
And use it to boost three toons on B-C-D.
You should have no issues with boosting three toons to at least 50th.
Rapidly run them through quests, once you reach an instance you cannot solo.

That gets you...
A) Level 60/61 Tank + Another 60 via granted levels from B.
B) Level 60/61 + Level 60 Boosted + Another 60 via granted levels from C.
C) Level 60/61 + Level 60 Boosted + Another 60 via granted levels from D.
D) Level 60/61 + Level 60 Boosted.

Then you have the option of boosting more, via the Tank on A.
Or leveling as a 4x group.

The boosting will get you a lot more teams, but only half as many toons on A.
And D will only have as many toons as you boost, since they aren't getting granted levels at all.
Still, you could boost quite a few teams, and easily have a Tank + Healer + 1-2 others on A.
And a lot of options on B-C, with several on D.
If you wanted, you could toon transfer from B/C to A/D.
Or just go with more toons from RAF on BC then AD.