I'm on a PvE server and have not done extensive BG/Arena with my team yet.
Still did the midsummer stuff over the weekend, and the team fared well in limited conflicts.

I'm running 4x Shaman and 1x Paladin; had 5x Shaman, but subbing the pally.

In pvp's, the fear bomb is a large threat to a boxer.
So are AoE type attacks, although you defenses against both.

I've heard Tremor totems pulse all at once on the server clock.
If this is true, there's no point in staggering their drops.
Still a fear will last a maximum of 3 seconds, with an even chance of 0, 1, 2, or 3 seconds.
I've had fear bombs that are ended immediately.
A tremor down will provide a lot more protection then basically any other composition vs fear bombs.

No matter what you make, you'll be ganked leveling up.
So composition doesn't make a huge difference there.

If you have an extra account, beyond your team, you can have an opposite faction character.
It has to be another account, if you're on a pvp realm.
Then you can do fun things like transfers between horde and alliance side.
Or add "friends" who took a particular interest in your team while leveling... so you can track them down the road.

I've personally taken one of shammies and dual spec'd.
This gets me a full blown pve healer when I want one for heroics or challenging content.

I've also taken the pally and dual spec'd.
Pally will be a Prot spec'd healer, from the article on arena junkies paladin sub-forum.
Haven't really done much with that yet, but will mess around with it for pvp's.
4x Elemental, with a high mitigation/high health healer.
No experience with this yet, so no clue how it will turn out.

Pallies and Shammies synergize very well.
They're all mana users and benefit from the same type of buffs.
Pally has Kings for the shammies and will have Sanctuary down the road - next patch this includes Kings buff built into it.
One mana totem, and a combination of cleansing/healing streams will be sufficient heals for non instance pve content.

Shammies can round robin Fire Nova (with a stun component), Thunderstorm (for pushback), Earthbind (for root/snare).
Fire elementals put out a lot of AoE punishment - took out a random group of four 80's, with my 71 pally + 4x 73 shammies over the weekend with a couple Fire Elementals.

Eventually Elemental Mastery with Flame Shock and Lava Burst will one-shot just about anyone.
Hammer of Justice can gimp a lot of toons, and if they don't trinket they're dead before it ends with shammy burst.
Even if it sucks initially, it will get better; its a tried a true combination.