He is a list of World Instances and levels per the WOW website.

Scarlet Monastery - 28 - 44
Razorfen Downs 33 - 41
Uldaman 36 - 44
Zul Farrak 42-50
Mara 40 - 52
Sunken Temple 45-54
BlackRock Depth 48-60
BlackRock Spire 53-61
Dire Maul 54-61
Strathome 56 -61
Scholomance - 56-61

As far as healers just depends on your team make up. I personally prefer Priest or Pallys. But i am bias I have 70's of both toons.