I play WHM a lot for end-game and all other content, though my main is MNK. I did 15 MND and 15 Piety, and had minor issues of people dying and I having a bunch of MP available (just couldn't keep up with the dmg that was being done to them). I recommend putting 30 MND in ur stats, because it maximizes your heals. Healing will get easier as you get used to the content your doing and once you get certain skills like Regen mentioned from others.

One of the things I highly recommend, is stay away from Spell Speed equips as much as possible. I used to stack as much as I could, which was great for getting spells off faster and more often, but MP drained quick, the stats to focus on for your gear is MND & crit. They are by far the most helpful. But this is just from my experiences, and I do a lot of my content with static groups, so I'm use to my group and party style, while your groups may be different and do content differently, so you just need to find your happy middle ground.