Good guide overall, but I'd like to point out a few things.
GH R1 is pretty similar to Max rank Heal if you compare their output, making Heal the cheaper and only slightly weaker option. As soon as you get the T2 bonus it'll do a nice job, but I wouldn't use it before that.
Renew Rank 3 has a 100% coefficient at ~95 Mana (Close to 10 Heal per Mana) . If Melee take heavy DoT (golemagg, surpression), it will most likely not be wasted. And after some time, even heal snipes will become less frequent as your raiding guild gathers experience. You can also cast it while running! Buff your locks between the packs, they will lifetap.
Lightwell:
Step 1: Find a (competent) warlock
Step 2: Become best friends
Step 3: Place lightwell before boss starts
Step 4: Get full mana
Free Healing!