I'm WHM and I got down Caduceus now, I know it's nothing, but it's still the Coil.
Well, I just need my hotbar, I have one for attacking and one for focused healing.
I have Swiftcast and Virus for the worst moments, but with some coordination you can manage to heal everything well.
I think SCH is a bit harder though, due to the pet managing...
If you want to do the healer, just remember two things:
1. Don't underestimate the work you do, if a dps fails you just deal a bit less damage, if a healer fail the whole party dies.
2. Don't panic, just learn step by step and find your own way to heal.
And please, don't do like some assh*les I encountered on DF, that have some other class at lv50 and don't want to leave their precedent job, like lv50 BLMs that join dungeons as WHMs and dps mobs making everyone die XD