If you don't have at least fairly high healing skill, you'll probably want to sub SCH for Light Arts to give it a booster, but it's not absolutely crucial. Enhancing skill is nice to have high for good boosts & barspells, but again, not crucial. Honestly, you'll probably want to sub SCH either way, it's by far the best sub for WHM in almost all situations.
The important thing for a WHM in delve is to be able to cure effectively for 45 minutes straight without resting much and without receiving much support. You'll have ballads a portion of the time, but can't really rely on them much. You'll want an idle build that has a good bit of refresh, and you'll want a cure build that has capped potency with AF3+2 legs equipped for MP returns. In addition to that, you'll want to work some fast cast / cure cast into your build so that you can cast faster as you'll be very busy for the whole 45 minutes. If your equipment is lacking, consider grabbing Ionis, it does offer a slight fast cast bonus among other things.
____________________________Pergatory (Asura, Kupo LS) WHM99 ~ SMN99 ~ DRK99 "If you want to know me, look inside your heart." -Lao Tzu