Nice read. Here's how I did this instance with 5 shamans:

For almost every group / boss:
- Deploy all totem before every attack (healing, mana, crit, grounding, etc) and redeploy them when needed (grounding)
- Stand at max range
- Target these enemies first: engineers, guards wielding 2-handed weapons and fel guards (use shocks when they're available and the enemy is in range to finish them off quickly)

Only Three fights in the instance require additional tactics:

The 3 engineer group
- Switch on 100% crit + racial + trinkets and drop them as fast as possible

The waves of fell orcs
- Deploy Stoneclaw totems at the start of every wave (if they're on cooldown wait with killing the last mob until they're available again)
- Kill the enraged orcs first (use shocks to kill them as fast as possible)
- Redeploy all your totems halfway through the fight, because they will expire
- If you're low on mana, just leave the last mob of a wave alive and use your watershield to regenerate mana

The last boss
- Make sure you redeploy the grounding totems before you kill the last of the caster group
- Dps him down before he does his aoe attack (risky, because he usually does this at his last percent of health anyway)

With decent gear you'll only need one or two mana breaks during this instance (should be possible to do it without any breaks, but I like to have full mana before I go into boss fights).