A few points:
- Make sure you are bonded with Lampas and Barghest so you get their red chest bonus (+10SP each). Additionally, make sure you're grabbing the silver chests for Compendium completetion. My memory's hazy, but you might be able to access one that gives you some bonus SP.
- Putting SP more then 1 or 2 levels into Will at this point is a bad idea. You should mainly try to put them into Max Vitality, which you can pair with the Silver ring (5% Vit regen every turn). You'll want to get a level in Agility as you move forward, with the ultimate goal of later in the game unlocking Vitality Regen, which requires max Magic Attack and Max level Vitality.
- As you've already said, tea buff is a big help before bosses.
- You want to end this fight as early as possible. The longer this goes on, the worse it gets. It's best to pop up a Morphine when the Tea Buff wears off. If you haven't at least almost gotten two Coffin Breakthroughs by the time it wears off, you're too slow.
- Break all the minor bindings before you Coffin Breakout, or else you'll take a massive amount of Lust damage.
- It doesn't matter if you get over 100 Lust as long as you've pressed the command for the 4th Coffin Breakout. After that, the fight will go into a scripted phase where your Lust doesn't matter. The tick damage will get impossible to keep up with after a few speedups, so you'll want to rush the last few through if you can.
And as always, if there's one fight to change the difficulty to Easy on, this is it. It won't affect any true ending requirements, and you can change it back afterwards. I can safely say the fight is 100% consistent on Easy, at least. Good luck!
Edit: Did you delete your post because you beat Iron Maiden before I posted this? Your post disappeared, lol