Personally i wouldn't go for anything below 65% Debuff. I once tried a 50% Debuff Team on a harder map but wasn't that pleased with the result.

20 % Damage Reduction is a lot.

Kerria
Aconite
Halloween Peony
Snowdrop
Lycoris Miko

That's definetely a good team. I know it's tempting to squeeze in another Monster Damage Unit in form of Rainbow Rose but like i said you would miss 20% Damage Reduction.

If you want to go the Aconite Route you have to buy a Japanese Novel if i remember correctly. It's something like 7 $.

In case you want to buy Aconite's Serial Code please let me know. I considered buying her for a long time now and i would do it if there is an easy uncomplicated way to do it. Maybe you figure out a way how we can get her easily