Kate,

Not sure why Hadronox is presenting a problem, I assume you're moving out of the poison right and cleansing your team as required?

Easy Heroics for 5xMelee (with say minimal, but not totally trashy gear)

DTK
UK (assuming follower-only movement is available for Ingvar phase 1)
OK
CoS

Those four I think would be doable for a 5xMelee team virtually in quest blues. AN is trickier because the first boss can run a team of off-healers out of mana if the DPS is low, and Anub'Arak is a right pain in the ass with his Pound attack that doesn't display his direction well.

As for the ICC 5mans (normal), none will be easy I reckon until the team has a little gearing.

Devourer of Souls will eat up poorly geared Melee in FoS. For PoS, Frick and Ick take some learning and Tyrannus is a small gear check. In HoR both encounters can run 5xMelee dry for mana (I'm assuming the 4xMelee are Ret Pallies doing off-healing for the tank).

Also, as to Boylstons comments.

I'd agree that 1xTank,4xDPS+off-healing works well for Heroics. If you never want to raid, you'll never need to change that.

However, if you do want to raid, or run in Cata from what we've heard so far, I'd recommend a dedicated healer. Either gear up first with 1xTank,4xDPS and then faceroll through Heroics to gear a Healer (what I'm doing right now), or go 1xTank,3xDPS,1xHealer from the get go.