Well right now I have a level 35 Gladiator with the basic miracle sword, a 36 level martial artist, a 35 level mage, and a 35 level priest. My Gladiator is fine because I'm using Double up to dramatically increase my attack and slightly lower my defence which I would then enhance using a buff spell as I don't have kabuff yet. With the prayer ring equipped and my miracle sword, the gladiator regains anywhere from 40-70 hp per turn. My martial artist isn't doing much for me though. My mage is only there to accelerate my squad and sap the boss to lower his defence. My priest is just there to heal but since I don't have multiheal, I can only heal one character per turn. I've managed to get far into the fight but as soon as I luck out and get the whole team hit consecutively, I can only heal one character significantly at a time and they start to die one by one.
Right now I'm just leveling my characters to 40 to then do their specific class quests. After that I'll change vocations and level them up again. I haven't done much material hunting because I'm finding it to be annoying specifically by the fact that I'm just getting tired of flipping through the large menu of weapons and whatnot, seeing what items I need and then having to come online to see a material map, then traveling there to harvest. I'm currently going through some DQ burnout unfortunately lol.
I do need to make some money though and purchase some of those mirror armors as you say they help out and my characters don't all have the top of the line armor at the moment.