So wait... tried to go back through the posts and think I'm confusing myself. Maybe Df~ can help me with the maths:
Sea Deity Neptune + Fortoytops: 75% Water Resist, 50% Dark, 50% Wood
Frost Devil: 3510 * .25 = 878
Blood Devil: 3690 * .5 = 1,845
Taur Devil: 3570 * .5 = 1,785
Pyro Devil: 3480
Harpie Devil: 3600
Total Damage Round 1 = 11,588
Vampires = 8,520 * .5 = 4,260 * 3 = 12,780
Berserk = 14,085 * .25 = 3,521
Highlander = 5,710 * .5 = 2,855
2,855 + 3,521 = 6,376 (for the same round hit, every 3 rounds)
2,855 guaranteed every round from Highlander
Sea Deity Neptune + Sea Deity Neptune: 75% Water, 75% Dark
Frost Devil: 3510 * .25 = 878
Blood Devil: 3690 * .5 = 923
Taur Devil: 3570
Pyro Devil: 3480
Harpie Devil: 3600
Total Damage Round 1 = 12,451
Vampire = 8520 * .25 = 2,130 * 3 = 6,390
Berserk = 14,085 * .25 = 3,521
Highlander = 5,710
5,710 + 3,521 = 9,231 (for the same round hit, every 3 rounds)
5,710 guaranteed every round from Highlander
Hell of a lot of consistent healing and heart chaining needed to bust through that.
So, the obvious conclusions here are that double Neptune makes the Vampire round much more manageable. But not particularly the Devil Round or the Berserk/Highlander. Guess the Triple Resist is the way to go. Needing a minimum of 12,780 hp to survive a linked up Vamps, and to be able to recover 12,780 hp in three rounds. RCV on my Neptune, Rainbow, Rainbow, StE team is only 1300... which means umm, need a lot of hearts. 600k HP on three Vamp Lords just seems like the bigger challenge to me and is where I failed earlier. The damage output on that team is just not very high at all. And it feels like I'll use tons of stones just to get through that phase.
Anyways, I know Df~ went through this exercise earlier, but sometimes it helps to step through it myself. If I messed up the numbers anywhere or overlooked an easy way to do it, let me know.