Progression behavior in P2 is pretty straightforward: make sure to maintain 100% uptime of Healing Rain, RT on cooldown (preferably on tanks and people with debuffs and Tainted Shadows), use your Tidal Waves for Healing Waves on tanks and healing absorbs, squeeze EB’s inbetween this all. Save your SG for when the add knocks the whole raid back and throw a few CH’s while in the air. This is the conservative way and saves a lot of mana, making you very effective in p3.
Towards the end of p2, you might want to use CH’s more often, depending on the HP level of your raid. But the prio is obviously to keep the tanks up. Personally, I think excessive use of CH in p2 is a waste, unless (a) raid is very low and Edict is incoming soon, or (b) you’re going for the ranks 😛
As for the cooldown usage, feel free to use Ascendance + SG on 1st Tempest, it will be ready in p3 again. Healing Tide + SLT handles one edict in p2 just fine. In case you’re running with Echo, I suggest you to use second SLT on Gavel in p3, together with Spiritwalker obviously (and second Ascendance).