Need advice - filling out 5th acct

[Ualaa]

Take the toon you want to level, plus another toon that is similar level.
And group the toons together.
I've found a mage (Arcane Explosion) to be one of the best toons to be in this group.

Take three Shaman characters from the other three accounts.
Group these together too.
If you can spec/dual-spec one of the Shammies as Resto (Earth Shield) that helps some.
You will want Stoneclaw Totem, on round-robin.
And Magma Totem x3 on a single press.

The best targets will be melee mobs (animals rock) who are 3-5 levels higher than your lowbies.
Have the three Shammies on auto follow behind the Lowbies.
Run the lowbies around, and aggro (Damage) a lot of mobs via Instant Cast (so you can cast while running) damage spells.
Don't bother to stop and cast until they hurt a mob, instead run through several groups and spam the spells.
The spammer should stack Stamina, not caring about anything else.
Earth Shield on the spammer helps, but is not essential.

Once you get a few (I did this on Rhino's in Borean Tundra, and considered 8-10 to be a "good pull"), drop your 3x Magma and 1x Stoneclaw Totems.
As soon as Stoneclaw is destroyed, drop the 2nd one.
Do the third if you need it.
Redeploy your Magma Totems as soon as they die.

Because your toons are in a group, and have tagged (damaged the mobs), they get full experience provided only pets or damage shields do the remaining damage.
If your toons are not grouped, this will not work.
If your higher level boosters do even 1 point of damage via direct spells or dots, this doesn't work.

I did 60th to 70th, on two toons in Borean Tundra (with 3x 80's boosting).
The entire process was 5 hours, and I looted 450 stacks of meat in the process.
Would have been faster without looting.
Did 1.50 levels of rested, in just under 30 minutes of killing.
The Rhinos were mid 60's, so it started slow... hard to damage them with Arcane Explosion and ended slow (well hard to call 30-45 minutes a level as slow, for the upper 60's).
When the lowbies were within a couple of levels of the Rhinos, the levels just flew.

You can search by type (Animal, etc) on wowhead and filter by level range.
To select where to kill things.

[katsurahama]

Wow this is a great answer. Thanks so much for your help.